
Explains the theory and associated mathematics of quantum mechanics, discussing topics ranging from uncertainty and time dependence to particle and wave states.
The good news is, as others have already suggested, this level of education is now very accessible by e.g. YouTube channels:
https://youtube.com/c/pbsspacetime
https://youtube.com/c/SabineHossenfelder
https://youtube.com/playlist?list=PL701CD168D02FF56F (Susskind, The Theoretical Minimum: Quantum Mechanics)
I would add the channels:
https://youtube.com/user/EugeneKhutoryansky
https://youtube.com/user/minutephysics
and the MOOC Brilliant.org
That said, I’m still definitely in the “undrergrad” level despite all this; I can recognise the equations of GR and QM, but not use them, and there’s plenty which I know I must be misunderstanding.