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...
Bitwarden just announced a consortium with Apple, Google, 1Password, etc to create a secure import/export format for credentials; spurred by the need for passkeys to be portable between password managers (but also works for passwords/other credential types)