I'm not sure of the meaning here. Is it:
a. ISA extensions can't be called by any program not written by Apple? (including Asahi)
b. Nobody else but Apple has the right to have these ISA extensions, but when in Silicon, programmers can use them?
c. Nobody else who licenses ARM would be allowed to add extensions to their implementation of the ISA in this way. Apple is more or less a founding member of ARM and has some other deal.
> Nobody else but Apple has the right to have these ISA extensions
Programmers "can" use Apple extensions because... they're extensions to the ISA, they're not documented but they can't really be blocked off unless they're ring0, and that would make them a lot less useful (the entire point of having extensions for matrix computation is to speed up matrix computations, which are not usually kernel work, and having to syscall to do them would waste the entire thing).