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 sucked, so we ended up ripping it all out...
I wish FIDO had paid more attention to SQRL. It’s long in the tooth now, but with some attention it could have been a better solution than passkeys, IMO.