We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda suck...
I use a password manager with passkey support and still disabled all my passkeys. The user experience for passkeys is so much worse even when support exists.
Using a security key as a password manager seems to resolve this issue (I think?), but I guess the issue is more a problem for the casual user who wouldn't bother with a security key!