There are synced passkeys, and there are device-bound passkeys. The OP mentions Yubikey: you can store a passkey on a Yubikey, and then it's device-bound and c

There are synced passkeys, and there are device-bound passkeys. The OP mentions Yubikey: you can store a passkey on a Yubikey, and then it's device-bound and can't be exported. But Apple's implementation of passkeys is synced; they're just stored in an encrypted keychain.