@cmbarton Sorry for some confusion I may have caused about the forum, and thanks to @DenBesten and @grb to “clean it up”. (I think in the future, I’ll look more often into the Discourse documentation…)
I just did so, just in case: MacOS and passkey usage with Bitwarden - continuation
That sounds encouraging! And should confirm, that it is possible!
I would add in general: unfortunately it is the case, that the implementation of passkeys on certain sites is far from perfect. So dependent on what sites you try it - there are cases in which it may not be your system if it doesn’t work, but more the “quirks” of the site.
(BTW, that’s also a reason I suggested the forum account, because it usually works well with passkeys…)
Interesting.
And it makes me think again, that it may be something with the system and/or configuration…
Just a thought, not a recommendation: you could delete your current forum account and start a new one without the “GitHub login”, if you want to avoid every confusion. Of course that would also have the side effect, that the reading and interaction time in the forum would be set to zero again… (BTW, if you can delete the forum account easily… there was/is a bug with the forum software, for some people not seeing the “delete account” button)
Another possibility would be to look for other accounts, you might be able to experiment with passkeys: https://passkeyindex.io and https://passkeys.directory provide lists of sites with passkey support. (“MFA” = a passkey as 2FA/MFA) – Though, as written above, it’s kind of a lottery, if the passkey implementation is good or bad. 
(personally, I certainly wouldn’t recommend eBay for testing passkeys…)
I can also see that… As @grb already wrote, “spam” is the main reason. Spam happens always here and there, but a few weeks ago, the forum “suffered” a massive spam attack, and the current settings were also a reaction to that incident, as far as I understand it.