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...
It depends on what kind you want to use. If you want the most security, you can store them on something like a Yubikey, with it only being on that device and not exportable. If you get a new device, you’ll need to add that new device to your accounts. For less security but more convenience, you can have them stored in a password manager that can be synced to some service (self-hosted or in the cloud) or has a database file that can be copied.
That’s fair. It can be a bit of a mess with different browser, OS, and password manager support and their interactions but it has continued to get better as there is more adoption and development.