Your mistake seems to be thinking that adding things to U2F credentials (here resident keys) doesn't make passkeys a superset, but that's what it does. Passkeys

Your mistake seems to be thinking that adding things to U2F credentials (here resident keys) doesn't make passkeys a superset, but that's what it does. Passkeys are U2F credentials with more stuff. The extra stuff makes passwordless possible, but whether it's allowed is up to the service. Either way, the user has a passkey. The roaming vs. platform distinction is much more arguable. Common use has "passkey" meaning "passwordless-enabled platform authenticator", but technically hardware keys also fit the bill. I stick with the common use for pragmatic reasons, but either side can well-acktshually the other all day on this one.