I just happen to have read Asahi Linux's description of the boot process on Apple Silicon yesterday, and I would disagree: indeed the tl;dr would be that it seems that components are highly segregated and unable to communicate with each other, for security and trust reasons.

IIUC this translates to the inability for a hypothetical POST stage to access anything to perform something resembling an actual POST, and even if it did, it would be unable to transmit any result to the later stage.

https://github.com/AsahiLinux/docs/wiki/Introduction-to-Appl...