Ok, so the problem was that there was a system variable called PYTHONPATH, which I don't remember setting. It seems that Chemdraw, if installed with ChemScript, installs it's own python installation, which is 2.X.
That python install seems to set its own system variable called PYTHONPATH, which Sublime seems to prioritize for it's default python build system.
Delete whatever incorrect path is set in PYTHONPATH and paste the following into it instead:
C:...\Python\Python39\Scripts;C:...\Python\Python39;C:...\Python\Launcher;
I've deinstalled and reinstalled a bunch of Python Versions and edited my system variables in order to clean up the quagmire of pip not being able to install packages to the right locations. Long story short: Sublime now can't find numpy (or any 3rd party module), because it somehow figured that the python 2.3 version that comes with ChemDraw is the one I really want to use, not the 3.9 version I had used previously.
I've tried a bunch of tutorials online (such as resetting everything to factory settings) however nothing seems to unlink the python build system from that python 2.3 version that came with ChemDraw. Even deinstalling everything and installing Sublime 4 keeps that association. Like...how?
So here's my problem: My build system for python is linked to the wrong python version and I don't know how to link it to the python 3.9 that's located in AppData/Programs.
How can I associate the python.exe of python 3.9 in AppData with my python Build System instead of the current python 2.3, which is located ProgramFiles?
How do I reset the python build system in Sublime Text 3 on WIndows 10?