There is zero chance that Apple doesn't have MacOS and iOS running on RISC-V in the lab.

They did that with x86 and Arm half a decade before any announcement about a switch, not to mention a number of other ISAs that didn't make it to shipping (e.g. M88k) and probably ones that word has never leaked about. IA64, anyone?

They're too large and rich and risk-averse to *not* do it.