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 hope I am not misunderstanding you. What you are worried about is passkeys in the password manager not syncing to new devices? They are though, with password managers that support passkeys like Bitwarden, 1Password etc…
Currently using it on Bitwarden, if I log in to a new device, the passkeys are there.
You understood correctly. Seems like I missed some news on the syncing front.