Your fingerprint and face never leave this device. They are never sent to any server, never stored online, and never shared. Signing in with a passkey is more private than typing a password.
Face ID / Touch ID produces a local yes/no. That unlocks a private key to sign a one-time challenge — the biometric itself is never transmitted.
Only a public key (non-secret by design), a credential ID, and a signature counter. Nothing that can impersonate you or be reversed into a biometric.