That's the thing that I find unconvincing about webauthn. There seems to be no other way than to associate several key devices for every website you are using if you are concerned about losing a key device (or get a new phone, new laptop w TPM).
Totally understood - you have to do it once per website per device but I get that's still a hassle. That said it doesn't have the UI quirks that (even good) password managers have.
