My passkeys are in my self-hosted Vaultwarden. If I can't put them there, I don't use them.

It's not all sunshine and roses, though. Despite having Bitwarden set as the only passkey provider in my Android setup, the phone persistently only offers me Google. Which is empty, because as I said, I won't use one tied to things I can't control. Works great on desktops, though.

Passkeys can theoretically require you to be on hardware, I haven't found anything yet that requires that.