Their AMX instructions, and those decompress instructions you found in user space are the exact kinds of things even regular architectural license holders aren't allowed to do, even hidden behind a library.
They very clearly have a special, Apple-only relationship with ARM.
AMX is available in userspace, but only used by their Accelerate.framework library. Apple does not document or expect them to be used by any apps, and I expect they'd reject any App Store submissions that use them, as I doubt they guarantee their continued existence in their current form in future CPUs.
FWIW, the compresssion instructions are used by the kernel, and I don't even know if they work from userspace. I've only ever tried them in EL2.
They very clearly have a special, Apple-only relationship with ARM.