IIRC, Apple uses 'platform' to refer to an SoC integration. For example, M1, M2 and etc. are separate platforms. M5 in Vision Pro is a separate platform than M5 in MacBook Pro. I believe Apple's XNU does somewhat still support non-Apple Silicon as well though.
Twice, on the basis that NEXT used the same kernel and that ran on 68k and Intel when Apple bought them and later ported it for Power PC. When Steve Jobs went back to Apple, for a long time he ran NEXT on a Thinkpad.
