> With plain venv it’s hard to maintain multiple different Python versions on the same machine;

plain venv never advertised itself as a solution to this problem... I don't like this tool, but, sorry to say so, you are barking on the wrong tree.

Also, it's not hard to maintain different versions of Python on the same machine without conda. I can literally do this with my eyes closed w/o touching the mouse: it boils down to:

    cd ~/src/cpython
    git checkout 3.8
    git fetch --all
    git reset --hard origin/3.8
    git clean -Xdf
    ./configure --with-ensurepip=install --with-system-ffi=yes
    make
    sudo make altinstall

Sorry. I've done this from memory and I kept one eye open. So, I kinda lied. But not really.