I'm still using xquartz (https://www.xquartz.org) on current machines - with the last release just a few weeks ago. But it's only for retro stuff. Other than that, X11 was never anything why I would buy a Mac for.

1) was a problem in the early days, but what they poured into clang did eventually pay off. It's a reasonable compiler with tons of vendor extensions, many being Apple's, these days. Clang also served as a source for GCC to take new features from. Good to have some competition.

2) XQuartz took a while, but is doing well.

3) was a big one in making upstream wine not work. with wine32on64 you can sure still pull the pinball party trick, but building that thing takes too much.

4) was specifically SIP for me, especially when they started making updates break with system changes. The ntfs-3g automount thing has always relied on replacing mount_ntfs [which is, by the way, not the proper way to make an fs on a Mac -- there's some filesystem bundle business], and now it's too much of a pain to still access the Windows drive.