diff --git a/CHANGES.rst b/CHANGES.rst
index 5717e48d..461284c0 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -21,6 +21,14 @@ Unreleased
 -   Support View and MethodView instances with async handlers. :issue:`4112`
 -   Enhance typing of ``app.errorhandler`` decorator. :issue:`4095`
 -   Fix registering a blueprint twice with differing names. :issue:`4124`
+-   Fix the type of ``static_folder`` to accept ``pathlib.Path``.
+    :issue:`4150`
+-   ``jsonify`` handles ``decimal.Decimal`` by encoding to ``str``.
+    :issue:`4157`
+-   Correctly handle raising deferred errors in CLI lazy loading.
+    :issue:`4096`
+-   The CLI loader handles ``**kwargs`` in a ``create_app`` function.
+    :issue:`4170`
 
 
 Version 2.0.1
diff --git a/docs/api.rst b/docs/api.rst
index e6862878..09fc71a9 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -256,7 +256,7 @@ the filter to render data inside ``<script>`` tags.
 
 .. sourcecode:: html+jinja
 
-    <script type=text/javascript>
+    <script>
         const names = {{ names|tosjon }};
         renderChart(names, {{ axis_data|tojson }});
     </script>
diff --git a/docs/deploying/asgi.rst b/docs/deploying/asgi.rst
index c7e04027..39cd76b7 100644
--- a/docs/deploying/asgi.rst
+++ b/docs/deploying/asgi.rst
@@ -5,7 +5,7 @@ ASGI
 
 If you'd like to use an ASGI server you will need to utilise WSGI to
 ASGI middleware. The asgiref
-[WsgiToAsgi](https://github.com/django/asgiref#wsgi-to-asgi-adapter)
+`WsgiToAsgi <https://github.com/django/asgiref#wsgi-to-asgi-adapter>`_
 adapter is recommended as it integrates with the event loop used for
 Flask's :ref:`async_await` support. You can use the adapter by
 wrapping the Flask app,
@@ -21,7 +21,7 @@ wrapping the Flask app,
 
     asgi_app = WsgiToAsgi(app)
 
-and then serving the ``asgi_app`` with the asgi server, e.g. using
+and then serving the ``asgi_app`` with the ASGI server, e.g. using
 `Hypercorn <https://gitlab.com/pgjones/hypercorn>`_,
 
 .. sourcecode:: text
diff --git a/docs/patterns/jquery.rst b/docs/patterns/jquery.rst
index fafbdf18..0a75bb71 100644
--- a/docs/patterns/jquery.rst
+++ b/docs/patterns/jquery.rst
@@ -23,8 +23,7 @@ to add a script statement to the bottom of your ``<body>`` to load jQuery:
 
 .. sourcecode:: html
 
-   <script type=text/javascript src="{{
-     url_for('static', filename='jquery.js') }}"></script>
+   <script src="{{ url_for('static', filename='jquery.js') }}"></script>
 
 Another method is using Google's `AJAX Libraries API
 <https://developers.google.com/speed/libraries/>`_ to load jQuery:
@@ -59,7 +58,7 @@ like this:
 
 .. sourcecode:: html+jinja
 
-   <script type=text/javascript>
+   <script>
      $SCRIPT_ROOT = {{ request.script_root|tojson }};
    </script>
 
@@ -109,7 +108,7 @@ usually a better idea to have that in a separate script file:
 
 .. sourcecode:: html
 
-    <script type=text/javascript>
+    <script>
       $(function() {
         $('a#calculate').bind('click', function() {
           $.getJSON($SCRIPT_ROOT + '/_add_numbers', {
diff --git a/docs/quickstart.rst b/docs/quickstart.rst
index b5071ab0..179c4103 100644
--- a/docs/quickstart.rst
+++ b/docs/quickstart.rst
@@ -626,7 +626,7 @@ Werkzeug provides for you::
     def upload_file():
         if request.method == 'POST':
             file = request.files['the_file']
-            file.save(f"/var/www/uploads/{secure_filename(f.filename)}")
+            file.save(f"/var/www/uploads/{secure_filename(file.filename)}")
         ...
 
 For some better examples, see :doc:`patterns/fileuploads`.
diff --git a/docs/tutorial/tests.rst b/docs/tutorial/tests.rst
index d8f2a931..f97d19df 100644
--- a/docs/tutorial/tests.rst
+++ b/docs/tutorial/tests.rst
@@ -270,7 +270,7 @@ messages.
 
         with app.app_context():
             assert get_db().execute(
-                "select * from user where username = 'a'",
+                "SELECT * FROM user WHERE username = 'a'",
             ).fetchone() is not None
 
 
diff --git a/docs/tutorial/views.rst b/docs/tutorial/views.rst
index 2d5a01d3..7092dbc2 100644
--- a/docs/tutorial/views.rst
+++ b/docs/tutorial/views.rst
@@ -91,18 +91,18 @@ write templates to generate the HTML form.
                 error = 'Username is required.'
             elif not password:
                 error = 'Password is required.'
-            elif db.execute(
-                'SELECT id FROM user WHERE username = ?', (username,)
-            ).fetchone() is not None:
-                error = f"User {username} is already registered."
 
             if error is None:
-                db.execute(
-                    'INSERT INTO user (username, password) VALUES (?, ?)',
-                    (username, generate_password_hash(password))
-                )
-                db.commit()
-                return redirect(url_for('auth.login'))
+                try:
+                    db.execute(
+                        "INSERT INTO user (username, password) VALUES (?, ?)",
+                        (username, generate_password_hash(password)),
+                    )
+                    db.commit()
+                except db.IntegrityError:
+                    error = f"User {username} is already registered."
+                else:
+                    return redirect(url_for("auth.login"))
 
             flash(error)
 
@@ -125,26 +125,25 @@ Here's what the ``register`` view function is doing:
 
 #.  Validate that ``username`` and ``password`` are not empty.
 
-#.  Validate that ``username`` is not already registered by querying the
-    database and checking if a result is returned.
-    :meth:`db.execute <sqlite3.Connection.execute>` takes a SQL query
-    with ``?`` placeholders for any user input, and a tuple of values
-    to replace the placeholders with. The database library will take
-    care of escaping the values so you are not vulnerable to a
-    *SQL injection attack*.
-
-    :meth:`~sqlite3.Cursor.fetchone` returns one row from the query.
-    If the query returned no results, it returns ``None``. Later,
-    :meth:`~sqlite3.Cursor.fetchall` is used, which returns a list of
-    all results.
-
 #.  If validation succeeds, insert the new user data into the database.
-    For security, passwords should never be stored in the database
-    directly. Instead,
-    :func:`~werkzeug.security.generate_password_hash` is used to
-    securely hash the password, and that hash is stored. Since this
-    query modifies data, :meth:`db.commit() <sqlite3.Connection.commit>`
-    needs to be called afterwards to save the changes.
+
+    -   :meth:`db.execute <sqlite3.Connection.execute>` takes a SQL
+        query with ``?`` placeholders for any user input, and a tuple of
+        values to replace the placeholders with. The database library
+        will take care of escaping the values so you are not vulnerable
+        to a *SQL injection attack*.
+
+    -   For security, passwords should never be stored in the database
+        directly. Instead,
+        :func:`~werkzeug.security.generate_password_hash` is used to
+        securely hash the password, and that hash is stored. Since this
+        query modifies data,
+        :meth:`db.commit() <sqlite3.Connection.commit>` needs to be
+        called afterwards to save the changes.
+
+    -   An :exc:`sqlite3.IntegrityError` will occur if the username
+        already exists, which should be shown to the user as another
+        validation error.
 
 #.  After storing the user, they are redirected to the login page.
     :func:`url_for` generates the URL for the login view based on its
@@ -200,6 +199,11 @@ There are a few differences from the ``register`` view:
 
 #.  The user is queried first and stored in a variable for later use.
 
+    :meth:`~sqlite3.Cursor.fetchone` returns one row from the query.
+    If the query returned no results, it returns ``None``. Later,
+    :meth:`~sqlite3.Cursor.fetchall` will be used, which returns a list
+    of all results.
+
 #.  :func:`~werkzeug.security.check_password_hash` hashes the submitted
     password in the same way as the stored hash and securely compares
     them. If they match, the password is valid.
diff --git a/examples/tutorial/flaskr/auth.py b/examples/tutorial/flaskr/auth.py
index bcd3c672..b423e6ae 100644
--- a/examples/tutorial/flaskr/auth.py
+++ b/examples/tutorial/flaskr/auth.py
@@ -60,21 +60,21 @@ def register():
             error = "Username is required."
         elif not password:
             error = "Password is required."
-        elif (
-            db.execute("SELECT id FROM user WHERE username = ?", (username,)).fetchone()
-            is not None
-        ):
-            error = f"User {username} is already registered."
 
         if error is None:
-            # the name is available, store it in the database and go to
-            # the login page
-            db.execute(
-                "INSERT INTO user (username, password) VALUES (?, ?)",
-                (username, generate_password_hash(password)),
-            )
-            db.commit()
-            return redirect(url_for("auth.login"))
+            try:
+                db.execute(
+                    "INSERT INTO user (username, password) VALUES (?, ?)",
+                    (username, generate_password_hash(password)),
+                )
+                db.commit()
+            except db.IntegrityError:
+                # The username was already taken, which caused the
+                # commit to fail. Show a validation error.
+                error = f"User {username} is already registered."
+            else:
+                # Success, go to the login page.
+                return redirect(url_for("auth.login"))
 
         flash(error)
 
diff --git a/examples/tutorial/tests/test_auth.py b/examples/tutorial/tests/test_auth.py
index 3ac9a12c..0bc0a9db 100644
--- a/examples/tutorial/tests/test_auth.py
+++ b/examples/tutorial/tests/test_auth.py
@@ -16,7 +16,7 @@ def test_register(client, app):
     # test that the user was inserted into the database
     with app.app_context():
         assert (
-            get_db().execute("select * from user where username = 'a'").fetchone()
+            get_db().execute("SELECT * FROM user WHERE username = 'a'").fetchone()
             is not None
         )
 
diff --git a/src/flask/app.py b/src/flask/app.py
index 8c3c39d4..301694ac 100644
--- a/src/flask/app.py
+++ b/src/flask/app.py
@@ -389,7 +389,7 @@ class Flask(Scaffold):
         self,
         import_name: str,
         static_url_path: t.Optional[str] = None,
-        static_folder: t.Optional[str] = "static",
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = "static",
         static_host: t.Optional[str] = None,
         host_matching: bool = False,
         subdomain_matching: bool = False,
diff --git a/src/flask/blueprints.py b/src/flask/blueprints.py
index c8ce67a4..5c23a735 100644
--- a/src/flask/blueprints.py
+++ b/src/flask/blueprints.py
@@ -1,3 +1,4 @@
+import os
 import typing as t
 from collections import defaultdict
 from functools import update_wrapper
@@ -175,7 +176,7 @@ class Blueprint(Scaffold):
         self,
         name: str,
         import_name: str,
-        static_folder: t.Optional[str] = None,
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
         template_folder: t.Optional[str] = None,
         url_prefix: t.Optional[str] = None,
diff --git a/src/flask/cli.py b/src/flask/cli.py
index d9e810da..0d101d0a 100644
--- a/src/flask/cli.py
+++ b/src/flask/cli.py
@@ -103,18 +103,21 @@ def call_factory(script_info, app_factory, args=None, kwargs=None):
         )
         kwargs["script_info"] = script_info
 
-    if (
-        not args
-        and len(sig.parameters) == 1
-        and next(iter(sig.parameters.values())).default is inspect.Parameter.empty
-    ):
-        warnings.warn(
-            "Script info is deprecated and will not be passed as the"
-            " single argument to the app factory function in Flask"
-            " 2.1.",
-            DeprecationWarning,
-        )
-        args.append(script_info)
+    if not args and len(sig.parameters) == 1:
+        first_parameter = next(iter(sig.parameters.values()))
+
+        if (
+            first_parameter.default is inspect.Parameter.empty
+            # **kwargs is reported as an empty default, ignore it
+            and first_parameter.kind is not inspect.Parameter.VAR_KEYWORD
+        ):
+            warnings.warn(
+                "Script info is deprecated and will not be passed as the"
+                " single argument to the app factory function in Flask"
+                " 2.1.",
+                DeprecationWarning,
+            )
+            args.append(script_info)
 
     return app_factory(*args, **kwargs)
 
@@ -312,7 +315,7 @@ class DispatchingApp:
         self.loader = loader
         self._app = None
         self._lock = Lock()
-        self._bg_loading_exc_info = None
+        self._bg_loading_exc = None
 
         if use_eager_loading is None:
             use_eager_loading = os.environ.get("WERKZEUG_RUN_MAIN") != "true"
@@ -328,23 +331,24 @@ class DispatchingApp:
             with self._lock:
                 try:
                     self._load_unlocked()
-                except Exception:
-                    self._bg_loading_exc_info = sys.exc_info()
+                except Exception as e:
+                    self._bg_loading_exc = e
 
         t = Thread(target=_load_app, args=())
         t.start()
 
     def _flush_bg_loading_exception(self):
         __traceback_hide__ = True  # noqa: F841
-        exc_info = self._bg_loading_exc_info
-        if exc_info is not None:
-            self._bg_loading_exc_info = None
-            raise exc_info
+        exc = self._bg_loading_exc
+
+        if exc is not None:
+            self._bg_loading_exc = None
+            raise exc
 
     def _load_unlocked(self):
         __traceback_hide__ = True  # noqa: F841
         self._app = rv = self.loader()
-        self._bg_loading_exc_info = None
+        self._bg_loading_exc = None
         return rv
 
     def __call__(self, environ, start_response):
diff --git a/src/flask/config.py b/src/flask/config.py
index c79a558e..ca769022 100644
--- a/src/flask/config.py
+++ b/src/flask/config.py
@@ -83,7 +83,7 @@ class Config(dict):
         :param variable_name: name of the environment variable
         :param silent: set to ``True`` if you want silent failure for missing
                        files.
-        :return: bool. ``True`` if able to load config, ``False`` otherwise.
+        :return: ``True`` if the file was loaded successfully.
         """
         rv = os.environ.get(variable_name)
         if not rv:
@@ -107,6 +107,7 @@ class Config(dict):
                          root path.
         :param silent: set to ``True`` if you want silent failure for missing
                        files.
+        :return: ``True`` if the file was loaded successfully.
 
         .. versionadded:: 0.7
            `silent` parameter.
@@ -185,6 +186,7 @@ class Config(dict):
         :type load: ``Callable[[Reader], Mapping]`` where ``Reader``
             implements a ``read`` method.
         :param silent: Ignore the file if it doesn't exist.
+        :return: ``True`` if the file was loaded successfully.
 
         .. versionadded:: 2.0
         """
@@ -209,6 +211,7 @@ class Config(dict):
         :param filename: The path to the JSON file. This can be an
             absolute path or relative to the config root path.
         :param silent: Ignore the file if it doesn't exist.
+        :return: ``True`` if the file was loaded successfully.
 
         .. deprecated:: 2.0.0
             Will be removed in Flask 2.1. Use :meth:`from_file` instead.
@@ -232,6 +235,7 @@ class Config(dict):
     ) -> bool:
         """Updates the config like :meth:`update` ignoring items with non-upper
         keys.
+        :return: Always returns ``True``.
 
         .. versionadded:: 0.11
         """
diff --git a/src/flask/json/__init__.py b/src/flask/json/__init__.py
index 5780e204..10d5123a 100644
--- a/src/flask/json/__init__.py
+++ b/src/flask/json/__init__.py
@@ -1,3 +1,4 @@
+import decimal
 import io
 import json as _json
 import typing as t
@@ -47,7 +48,7 @@ class JSONEncoder(_json.JSONEncoder):
         """
         if isinstance(o, date):
             return http_date(o)
-        if isinstance(o, uuid.UUID):
+        if isinstance(o, (decimal.Decimal, uuid.UUID)):
             return str(o)
         if dataclasses and dataclasses.is_dataclass(o):
             return dataclasses.asdict(o)
@@ -117,6 +118,9 @@ def dumps(obj: t.Any, app: t.Optional["Flask"] = None, **kwargs: t.Any) -> str:
         or defaults.
     :param kwargs: Extra arguments passed to :func:`json.dumps`.
 
+    .. versionchanged:: 2.0.2
+        :class:`decimal.Decimal` is supported by converting to a string.
+
     .. versionchanged:: 2.0
         ``encoding`` is deprecated and will be removed in Flask 2.1.
 
@@ -324,6 +328,9 @@ def jsonify(*args: t.Any, **kwargs: t.Any) -> "Response":
     debug mode or if :data:`JSONIFY_PRETTYPRINT_REGULAR` is ``True``,
     the output will be formatted to be easier to read.
 
+    .. versionchanged:: 2.0.2
+        :class:`decimal.Decimal` is supported by converting to a string.
+
     .. versionchanged:: 0.11
         Added support for serializing top-level arrays. This introduces
         a security risk in ancient browsers. See :ref:`security-json`.
diff --git a/src/flask/scaffold.py b/src/flask/scaffold.py
index e80e1915..42eabcfc 100644
--- a/src/flask/scaffold.py
+++ b/src/flask/scaffold.py
@@ -92,7 +92,7 @@ class Scaffold:
     def __init__(
         self,
         import_name: str,
-        static_folder: t.Optional[str] = None,
+        static_folder: t.Optional[t.Union[str, os.PathLike]] = None,
         static_url_path: t.Optional[str] = None,
         template_folder: t.Optional[str] = None,
         root_path: t.Optional[str] = None,
@@ -101,7 +101,7 @@ class Scaffold:
         #: to. Do not change this once it is set by the constructor.
         self.import_name = import_name
 
-        self.static_folder = static_folder
+        self.static_folder = static_folder  # type: ignore
         self.static_url_path = static_url_path
 
         #: The path to the templates folder, relative to
@@ -257,7 +257,7 @@ class Scaffold:
             return None
 
     @static_folder.setter
-    def static_folder(self, value: t.Optional[str]) -> None:
+    def static_folder(self, value: t.Optional[t.Union[str, os.PathLike]]) -> None:
         if value is not None:
             value = os.fspath(value).rstrip(r"\/")
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index ebf8d1f5..e7462bde 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -17,6 +17,7 @@ from flask import Blueprint
 from flask import current_app
 from flask import Flask
 from flask.cli import AppGroup
+from flask.cli import DispatchingApp
 from flask.cli import dotenv
 from flask.cli import find_best_app
 from flask.cli import FlaskGroup
@@ -73,6 +74,15 @@ def test_find_best_app(test_apps):
     assert isinstance(app, Flask)
     assert app.name == "appname"
 
+    class Module:
+        @staticmethod
+        def create_app(**kwargs):
+            return Flask("appname")
+
+    app = find_best_app(script_info, Module)
+    assert isinstance(app, Flask)
+    assert app.name == "appname"
+
     class Module:
         @staticmethod
         def create_app(foo):
@@ -310,6 +320,23 @@ def test_scriptinfo(test_apps, monkeypatch):
     assert app.name == "testapp"
 
 
+def test_lazy_load_error(monkeypatch):
+    """When using lazy loading, the correct exception should be
+    re-raised.
+    """
+
+    class BadExc(Exception):
+        pass
+
+    def bad_load():
+        raise BadExc
+
+    lazy = DispatchingApp(bad_load, use_eager_loading=False)
+
+    with pytest.raises(BadExc):
+        lazy._flush_bg_loading_exception()
+
+
 def test_with_appcontext(runner):
     @click.command()
     @with_appcontext
diff --git a/tests/test_json.py b/tests/test_json.py
index fb8bdcba..9210275a 100644
--- a/tests/test_json.py
+++ b/tests/test_json.py
@@ -1,4 +1,5 @@
 import datetime
+import decimal
 import io
 import uuid
 
@@ -187,6 +188,11 @@ def test_jsonify_uuid_types(app, client):
     assert rv_uuid == test_uuid
 
 
+def test_json_decimal():
+    rv = flask.json.dumps(decimal.Decimal("0.003"))
+    assert rv == '"0.003"'
+
+
 def test_json_attr(app, client):
     @app.route("/add", methods=["POST"])
     def add():
