Thanks for posting this follow-up! Might you be willing to expand a bit on what you heard from Apple and whether/how you got it working? I've tried starting with IOServiceMatching("IODPDevice"), but I still get a null iterator—and there's nothing like IODPDevice in ioreg's output.
Otherwise, the only option I've found for getting any EDID info on an M1 appears to be to use CoreDisplay, but I'd rather use something documented.