One of my favourite unreported MacOS issues comes from how, at some point, they changed the appearance of the window close button to be a particular shade of red with a tiny little X in the center. And if you happen to be using a particular kind of screen and possibly wearing glasses, that little X kind of wanders around in the button, appearing just slightly off center in a maddening way. Made only more maddening by…
Another irritating thing that is captured in that image is the single pixel gap between the top of the application window and the menu bar. If the desktop background is bright it is very distracting. Not a mistake like the off centre X but drives me mad, nevertheless.
This is the same reason why window gaps are so popular in all tiling window managers. It just looks better.