That’s great news (and you get an award for the successful fight with the forum software 
) and yeah, so at least it’s possible.
Did you see this post, reporting that logging in to GitHub with a passkey from Bitwarden worked on the Mac?
I’m not sure, maybe it’s a bug - maybe you could try to deinstall/reinstall the extension, that sometimes helps (Sorry, if you have done it before, I seem to have forgotten it then by now). – My gut feeling tends to it’s a configuration issue (possibly something we are not aware of right now)… especially, since it work’s for @DoctorB - so what’s the difference with your configuration/settings so that it doesn’t work with GitHub?!
(It’s also anecdotal evidence, but apart from one or two reports here and there - we haven’t seen widespread reports about Bitwarden/passkeys/MacOS not working here in the forum.)
I think I provided the link before… here you can report bugs (“New issue”): GitHub · Where software is built If you report it, they will try to reproduce it. If they can’t reproduce the/a bug, the report will get closed very soon. Either way, you probably would get some clarity. (PS: though, again, if it works for @DoctorB , chances are, it’s not a general and widespread “malfunction”/“defect”… could still be a bug, happening under certain circumstances… unfortunately, those might be very difficult to track down…)
Can you provide the links?