Websites already have a hard time to get users to sign up, so requiring them to enroll backup authenticators (which they won't have) is not going to work. Printing or writing down backup codes is even worse from a UX point of view.
IIRC the spec has a flag to hint that the passkey is backed up (in iCloud or your Google account) so the relying party (website) knows whether backups are mandatory but that means the secret doesn't stay on your device and goes to the mothership. Then I don't see why the spec wouldn't standardize the transfer of secrets from one company to the other.
Websites already have a hard time to get users to sign up, so requiring them to enroll backup authenticators (which they won't have) is not going to work. Printing or writing down backup codes is even worse from a UX point of view.
IIRC the spec has a flag to hint that the passkey is backed up (in iCloud or your Google account) so the relying party (website) knows whether backups are mandatory but that means the secret doesn't stay on your device and goes to the mothership. Then I don't see why the spec wouldn't standardize the transfer of secrets from one company to the other.