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 use passkeys and find them great, mind you I know that you need at least 2 of them so you have a backup. I also use yubikeys at work and they are the same issue, you need 2 of them in case 1 breaks or gets lost.
Maybe the setup should be, make sure you have 2 passkeys on 2 different devices? but not in your password manager
Still, it makes adding new devices much more of a hassle.