Does it matter? Apple to my understanding has designed all of their Arm processors from the ground up around the Arm ISA for many many years now. They have extended its capabilities themselves, through their GPU cores, neural engine cores, they've designed specialized high and low power cores, they've developed a shared memory fabric. They don't need the base Arm ISA to do anything else -- Is x86_64 changing any time soon?What's to stop NVidia from forking the instruction set?
NVIDIA wants Arm to do more with in enterprise computing/HPC/AI, IMHO, than it has been embraced for traditionally. The #1 supercomputer in the Top 500 HPC systems is Fugaku, which uses Fujitsu Arm ISA chips I believe. But there aren't many Arm HPC systems, and NVIDIA probably thinks they can go after that space to take over the territory IBM seems to be ceding with POWER. Same with the hyperscalers (cloud providers). Apple has proved the Arm ISA can make for very efficient CPUs, but isn't likely to go after the space NVIDIA really wants to occupy any time soon. It's hard to imagine PC gaming making the shift to Arm. Maybe Apple did say "why don't you talk to NVIDIA."