.
├── doc
│   ├── conf.py
│   └── index.rst
├── myapp
│   ├── app.py
│   └── __init__.py
└── setup.py

# file: setup.py
from distutils.core import setup
setup(name="myapp", packages=["myapp"])

# file: myapp/app.py
from flask import Flask
from flask import request   # <------- This line triggers the exception!
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

# file: doc/conf.py
extensions = [
    'sphinx.ext.autodoc',
]

templates_path = ['_templates']
source_suffix = {'.rst': 'restructuredtext'}
master_doc = 'index'
project = 'hello'

.. file: doc/index.rst

.. automodule:: myapp.app
   :members:
   :undoc-members:
   :show-inheritance:

# requirements.txt
alabaster==0.7.12
Babel==2.9.0
certifi==2020.12.5
chardet==4.0.0
click==7.1.2
docutils==0.16
Flask==1.1.2
idna==2.10
imagesize==1.2.0
itsdangerous==1.1.0
Jinja2==2.11.2
MarkupSafe==1.1.1
myapp==0.0.0
packaging==20.8
pkg-resources==0.0.0
Pygments==2.7.3
pyparsing==2.4.7
pytz==2020.5
requests==2.25.1
snowballstemmer==2.0.0
Sphinx==3.4.2
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==1.0.3
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.4
urllib3==1.26.2
Werkzeug==1.0.1

$ # Create the files and structure above, then:
$ python3 -m venv env
$ ./env/bin/pip install -r requirements.txt
$ (cd doc && ../env/bin/sphinx-build -b html -T . output)

Running Sphinx v3.4.2
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 1 source files that are out of date
updating environment: [new config] 1 added, 0 changed, 0 removed
reading sources... [100%] index
Traceback (most recent call last):
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/cmd/build.py", line 280, in build_main
    app.build(args.force_all, filenames)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/application.py", line 352, in build
    self.builder.build_update()
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 298, in build_update
    len(to_build))
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 310, in build
    updated_docnames = set(self.read())
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 417, in read
    self._read_serial(docnames)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 438, in _read_serial
    self.read_doc(docname)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 478, in read_doc
    doctree = read_doc(self.app, self.env, self.env.doc2path(docname))
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/io.py", line 221, in read_doc
    pub.publish()
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/core.py", line 218, in publish
    self.settings)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/io.py", line 126, in read
    self.parse()
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/readers/__init__.py", line 77, in parse
    self.parser.parse(self.input, document)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/parsers.py", line 104, in parse
    self.statemachine.run(inputlines, document, inliner=self.inliner)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 171, in run
    input_source=document['source'])
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/statemachine.py", line 242, in run
    context, state, transitions)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/statemachine.py", line 459, in check_line
    return method(match, context, next_state)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2342, in explicit_markup
    nodelist, blank_finish = self.explicit_construct(match)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2354, in explicit_construct
    return method(self, expmatch)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2097, in directive
    directive_class, match, type_name, option_presets)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2146, in run_directive
    result = directive_instance.run()
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/ext/autodoc/directive.py", line 146, in run
    documenter.generate(more_content=self.content)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/ext/autodoc/__init__.py", line 959, in generate
    self.document_members(all_members)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/ext/autodoc/__init__.py", line 821, in document_members
    for (mname, member, isattr) in self.filter_members(members, want_all):
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/ext/autodoc/__init__.py", line 734, in filter_members
    if ismock(member):
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/sphinx/ext/autodoc/mock.py", line 156, in ismock
    if not hasattr(subject, '__sphinx_mock__'):
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/werkzeug/local.py", line 347, in __getattr__
    return getattr(self._get_current_object(), name)
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/werkzeug/local.py", line 306, in _get_current_object
    return self.__local()
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/flask/globals.py", line 38, in _lookup_req_object
    raise RuntimeError(_request_ctx_err_msg)
RuntimeError: Working outside of request context.

This typically means that you attempted to use functionality that needed
an active HTTP request.  Consult the documentation on testing for
information about how to avoid this problem.

Exception occurred:
  File "/home/users/malbert/tmp/sphinx-bug/env/lib/python3.6/site-packages/flask/globals.py", line 38, in _lookup_req_object
    raise RuntimeError(_request_ctx_err_msg)
RuntimeError: Working outside of request context.

This typically means that you attempted to use functionality that needed
an active HTTP request.  Consult the documentation on testing for
information about how to avoid this problem.
The full traceback has been saved in /tmp/sphinx-err-jzo0zc61.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!