> I assume this is referring to the tweet from the launch of the M1 showing off that retaining and releasing an NSObject is like 3x faster. That's more of a general case of the ARM ISA being a better fit for modern software than x86, not some specific optimization for Apple's software.

It's not really even the ISA, mainly the implementation. Atomics on Apple cores are 3x faster than Intel (18 cycles back to back latency vs 6). AMD's atomics have 6 cycle latency.