The multiple venv for different Python versions sounds exactly like what tox does
Then setup a github action that does nightly builds. Which will catch issues caused by changes that only tested against one python version or on one platform
py313 is a good version to test against cuz there were many modules removed or depreciated or APIs changed
good luck. Hope some of my advice is helpful
Just activate the venv and then put it out of your mind. Can activate it with either a relative or absolute path. Doesn’t matter which