i certainly don’t agree that system utilities and libraries are outside of that limit and said as much when i commented on Debian GNU/kFreeBSD: its its own thing… its neither debian, nor freebsd. it is however based on both

the gui is definitively part of the operating system - confirmed by that wikipedia page that you linked (though i’d say only in the case where the gui is heavily tied to the default configuration of the OS like windows, macos, android, etc), and that’s nowhere near the kernel