In python 3.9.9, as provided by the python.org macOS installer,

$ /Library/Frameworks/Python.framework/Versions/3.9/bin/python3
Python 3.9.9 (v3.9.9:ccb0e6a345, Nov 15 2021, 13:29:20) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import platform
>>> platform.mac_ver()
('10.16', ('', '', ''), 'x86_64')

As a result, packaging 21.3 (and packaging main HEAD) do not include ...11_0... in packaging.tags.sys_tags().
However, wheel happily builds wheels with this tag, which pip (e.g. latest, 21.3.1) then refuses to install.

As platform.mac_ver() cannot be retroactively changed for released versions of Python, this should be addressed in packaging to make the support for macOS 11.x from #319 more robust.

Reference: https://trac.sagemath.org/ticket/33155