Set python version on MacOS Big Sur

At least with MacPorts, this is done with the python_select command. It may not be immediately applicable to your setup (you didn't mention MacPorts) but it's somewhere to start.

From python docs noting that they seem to have hard coded 2.5 instead of the current version and is not that well written

What you get after installing is a number of things:

A MacPython 2.5 folder in your Applications folder. In here you find IDLE, the development environment that is a standard part of official Python distributions; PythonLauncher, which handles double-clicking Python scripts from the Finder; and the “Build Applet” tool, which allows you to package Python scripts as standalone applications on your system.

A framework /Library/Frameworks/Python.framework, which includes the Python executable and libraries. The installer adds this location to your shell path. To uninstall MacPython, you can simply remove these three things. A symlink to the Python executable is placed in /usr/local/bin/.

so remove

/Applications/Python 3.1
/Library/Frameworks/Python.framework/Versions/3.1
/usr/local/bin/python31 (I use a different install so this might be python3.1 or similar)