One thing that drives me nuts is just how they refuse to take the time and update all the settings pages to the new style. I don't hate the new style, in fact I think it is pretty okay (better than macos and KDE in some things, worse in others).
Like if you dig even slightly below the surface you get a dialog window straight from windows 95. Network settings for example, something I routinely have to deal with. It is absurd VPN companies make full-blown windows desktop software to tweak VPN settings on your PC because the default windows UI is so crap.