I have installed python 3.8.6 with homebrew on macOS. But when I check with which -a python3 I only get paths of 3.9 and 3.8.2.
Is there a way to find the paths of all versions installed by homebrew? Or maybe more general question, how can I find the path of 3.8.6?
Use brew info <packagename>
it's probably in one of (and referenced in both)
/usr/local/Cellar/python@3.8/3.8.6_2
/usr/local/opt/python@3.8/libexec/bin
See also Apple SE Where can I find the installed package path via brew
If it's not there, it's plausible the version detection is wrong and only searches for the first two version digits (as conflicting versions may clobber each other). In this case, follow the warning and reinstall the specific version you want.