NeXT was, but Carbon and its remnants were not produced at NeXT. Carbon is long gone, but those remnants still exist in iTunes/the various apps split off from it.

And being multiplatform doesn’t suggest the absence of platform-specific code. I’ve hypothesized recently (to some chagrin) that Apple probably still maintains a skunkworks version of macOS for PPC, as insurance. It would be silly if they didn’t, given the history. So, probably yeah there’s a bunch of PPC code in macOS, but I’d bet it’s generally quite identifiable.

I don't know why they would do that now. They're doing their own ARM thing, and the contingency would surely be more x86, even if not from Intel.

I don’t know why there would be a “the” contingency, but we know they’re also hiring for active RISC-V engineers. It’s definitely not obvious the field is as limited as that.

Yeah. Makes no sense. I loved PPC (and 68k before that) but it’s a dead platform that Apple has no interest in.

It’s not strong on embedded, mobile or desktop, debunked by x86 and now ARM on super computer, cloud and enterprise. If it’s not dead, it’s on life support.

ARM wasn’t strong on many of the platforms it’s now running and will be soon. Apple has historically backed weak hardware platforms both to a fault and to astonishing success. Part of the way they did that was maintaining cross ISA builds internally for platforms no one would bet on.

ARM has been on the rise since its creation. Gaining market share and entering new segments.

PPC has ben bleeding costumers since Apple left the boat. Even game consoles gave up. With RISC-V on the table, competition is even harder these days.

Why would it be emulated?

Maybe we’re not taking about the same thing. You’re saying there’s PPC code running on current macOS. If it’s running on recent hardware, it’s running emulated, since Apple hasn’t shipped a PPC machine in more than a decade.

I’m saying the exact opposite: that there’s likely PPC source code in macOS still maintained just in case. I really doubt all of the Carbon remnants are ISA specific, the point of bringing that up was that macOS’s roots are not entirely NeXT and things that still exist are based on APIs largely from classic Mac OS.

I really doubt they are maintaining a PPC fork. It's not a trivial effort and it would be hard to justify the investment and even harder to motivate the talent needed.

ISA specific code is restricted to kernel and drivers. What's left of Carbon has been through 3 transitions (PPC to x86, x86 to x64 only, x64 to ARM). It's ISA clean all right.

The linux kernel is multiplatform, and is full of ISA-specific code. They are not exclusive.