[johnklos]

No idea about Windows. No interest, either.

UEFI makes it so you can boot your Unix OS, like NetBSD, without needing to have specific bootblocks that are tailored to the given machine. You can move drives between Arm machines, too. Much simpler.

[JdeBP]

OpenBSD, too. I haven't tried FreeBSD on EFI on arm64 yet, but FreeBSD has done EFI on amd64 since version 10.