Ok; seems the compilation of different Python interpreter versions is more complicated than I thought. Sorry.
In my case, I had stumbled into the Python3: ImportError: No module named '_ctypes' when using Value from module multiprocessing problem; after
sudo yum install libffi-devel
(on my CentOS box), the newly built Python 3.8.5 was fine.
I'm afraid I don't have the expertise about resolving such issues in a generic way.
Do we have a contribution documentation anywhere?