You have to re-install all of your packages when you upgrade to a new major version of Python.  You'll need to pip3 install xxxx again.
I was finally able to get python 3.9.0 installed(was using 3.4.2) on my raspberry pi, however I cannot use pygame now stating "ModuleNotFoundError: no module named 'pygame'. I know where pygame is located, but I have no idea how to get python 3.9.0 to see where it is to read it.
Newer version of python cannot find module pygame