Here's an big update:
Since I have a 2019 model and a new 2024 (that I used Migration to absorb all the 2019's info) and both are riddled with Apple Music app troubles, I decided to factory reset the 2019 and see how the Apple Music app performs after that.
I did it a few days ago. So far, the Apple Music app works perfectly. I fully updated to Sequoia after the reset. Then I connected the two MacBooks by Wi-Fi, NOT Migration, and transferred all of my 55,000 music tracks to the reset 2019 MacBook. Everything works perfectly, no bugs at all. I can only assumed that what was originally buggy on the 2019 model got transferred to the 2024 model through Migration. But the bugs shouldn't have existed in the first place.
I realize this is no good solution for most people. But this is what happened. I'll update again soon after giving it more time to (hopefully not) go bad again.
I also intend, once the 2019 model proves completely un-bugged, to factory reset the 2024 model and then return all music tracks to it...and all my files...and re-set all my settings. HUGE time investment.