Not OS stuff
Apple likes grandiose operating system features, not modular libraries with well defined abstraction layers. QuickDraw, QuickDraw 3D, QuickTime, Quartz, Core Image, Core Animation, Metal, AVKit, etc. These systems tie heavily into the operating system so they can't be maintained for long. VR/AR is not easy. The time it takes Apple to finish the system is longer than they can maintain the system. The Vision Pro will be ready just as the hardware that can run it is obsolete.
https://developer.apple.com/documentation/technologies for the vast array of aging, starting, and overlapping APIs.
A bunch of other developers will build modular libraries that get VR/AR running on Windows and Linux. Those libraries might initially crude compared to Apple's but they'll live on and evolve.