It seems that macOS has gotten completely bogged down (like really, really bogged down) and mired in bureaucracy.
What I just described is a "little thing" that's very very hard to quantify to non-engineers, sadly.
(I recently learned (I have no exposure to Apple, I'd like to but their stuff is expensive!!) that you can't just "go ahead and upgrade Xcode", but that you have to do it in a very specific/esoteric way or you break absolutely everything, and that it's not unreasonable sometimes to just nuke macOS from orbit and green-field reinstall everything.)
Some of them are sloppy glitches in functionality or display, others have to do with poor stability (force closing more often). Never encountered any of these issues on iOS a few years ago.
The iOS-using products are Apple's cash cow. It does make sense that they'd prioritize working on iOS. However, what doesn't make sense is that Apple certainly has enough resources to work on both OSes. It's not like they don't have enough money to hire good developers.
That is the complaint, however. It makes some sense, except that Apple could easily afford to invest in both macOS and iOS.