Apple has always chosen form over function, and this isn't any exception; the aesthetics of a "clean" boot process is clearly more important to them than being able to easily figure out what's happening, and I suspect at least part of the reason for this opaqueness is to encourage learned helplessness and visits to the Apple Store (which may result in upselling or otherwise exchange of $$$) when something doesn't wor…
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...