If you are trying to use WebauthN for unlocking your vault, unfortunately that is not supported by Bitwarden, at least not yet. There is an active feature request for this, however, if you are interested to support it:
You can use Webauthn for two-factor authentication, of course (not sure if that was your intention - sorry). But I don’t know if Android phones can be used as a second-factor device or not - I haven’t seen support for this, but the Bitwarden folks have been adding a lot of new features lately.