Here's one small change to macOS that drives me nuts. At some point they changed how application hiding works.
It used to be that cmd-h hid an application and moved it to the end of the application stack. If you wanted it back you could use cmd-shift-tab.
Some suit, in their wisdom, decided to change that so cmd-h now only hides the app.
It's a tiny change ...that's a stone in my shoe every single day. IMHO that change is was completely unnecessary and breaks my workflow.
Between each significant revision of Apple's desktop OS, my mother would get frustrated at settings that were moved elsewhere/renamed/removed entirely, for example. OSX is no stranger to unnecessary changes (or at least that's what my mother thinks of them).