After some trial and error I upgraded, pip, distlib and setuptools and it solved it. Not sure which of those is causing it. (On the last two I found issues 1 2 of other sites)
It is caused by removing unescape from HTMLParser in python3.9, which seems to break setuptools.
pip3 install --upgrade setuptools
If it does not work, try also:
pip3 install --upgrade pip
pip3 install --upgrade distlib
Note from @seb comment: The default pip3 may not be the python you are using. If so, try pip of your specific version used (e.g. pip3.9)