So are Meta publishing standards, gratis or not, which I can implement to create a compatible operating system?
I'm asking because it seems to me from this press release that they're just letting a handful of hardware partners use their software, which is not open in the sense of POSIX Open Group.
Yes, open like that. I thought we'd already established the sense in which Open Group is open, but you still haven't addressed the question how Meta is open in the same sense.