Discourse recently added support for passkeys for authentication; I’ve been able to add them to my accounts on a number of other Discourse sites, but there’s no “Add Passkey” button in the Preferences->Security panel on this site.
It’s possible that this new feature hasn’t been rolled out to all Discourse sites hosted by CDCK yet, or that it has to be enabled by the site admins, or something else entirely 
In any case, if it can be enabled, I’d certainly appreciate it.
I’ve added Yubikeys to my account, the /u/$USER/preferences/security page has a link to “Manage Two-Factor Authentication” at /u/$USER/preferences/second-factor and that page has a “Add Physical Security Key” link.
You might need to setup 2FA first?
No, 2FA is not required to use Passkeys; they are independent.
I had a quick look and there’s nothing matching “passkey” as a search in the admin settings, so I can only hope it hasn’t reached us yet!
Sorry I hadn’t realised that Passkeys are different from Security Keys 
, looks like it’ll need a newer version of Discourse or perhaps it can already be enabled using the rails console: