> MacOS is proprietary

Some of the drivers are. The core is open source, though. macOS' particular choice for its graphical user land is proprietary as well, but AT&T's UNIX had no such equivalent, aside from some experiments, so that doesn't make sense to use as a point of comparison. Not to mention similar systems in the UNIX-esq space, like SunView, NeWS, VUE, NeXTSTEP, etc. were proprietary too. That has always been par for the course in the world of "graphical UNIX". The so-called "Linux desktop" is the aberration.

You can, of course, run an open source graphical user land, like Gnome, instead on top of macOS' UNIX-y fashioned bits if you so wish.