The platform/local authenticator implementation currently allows user verification by means of Touch ID biometrics, with a fallback to account passwords for cases when Touch ID is not easily available (clamshell mode or hard to reach sensor). It would be convenient if the local authenticator also allowed verification using Apple Watch. Apple Watch is already available as a screen unlock method and in other verifying contexts in MacOS, so it would seem reasonable to also make this possible in WebAuthn. It offers good usability, especially in clamshell mode when passord taping is the only other alternative. For reference, Chromium has supported Apple Watch for WebAuthn for a while now: https://bugs.chromium.org/p/chromium/issues/detail?id=1002526#c11