It's all a bit "almost, but not quite", isn't it?
#FreeBSD has trouble with more than 4GiB of RAM on the #RaspberyPi 4, and does not even acknowledge the 5 (from 2023) in its doco.
#NetBSD does not support the Raspberry Pi 5 yet, has a 3GiB limit on the 4, and in its doco encourages EFI bootstrap, using a TianoCore port, over a more direct method.
But the Pi bootstrap that loads the EFI firmware doesn't support the EFI partition table, so one has to go back to using the old "MBR" one.
And USB doesn't work because the stock NetBSD build doesn't include pci drivers for the Pi. So one has to re-cross-compile the operating system.
#OpenBSD encourages EFI firmware, too, and has a workaround for the 3GiB DMA problem, but likewise the Pi 5 is alien to its doco.
The hardware vendor points at its own operating system, of course, which hides the details behind opaque tooling and whose doco calls such details "legacy".