FIDO2 supports "PINs" (can be a passphrase) but it's opt-in because you have to distribute devices to users - if you put a default PIN, it's like having no PIN.

FIDO2 supports "PINs" (can be a passphrase) but it's opt-in because you have to distribute devices to users - if you put a default PIN, it's like having no PIN. So it seems to me that what you're asking is there already. Just maybe not advertised as it should. Am I missing something?