I have recently enabled the SMS Passwordless connection with New Universal Login. As it now works when
Identifier First + Biometrics is set, I expect that signing in with SMS passwordless would enable me to enroll for device biometrics. I quickly tested it out, but it did not work as expected.
Using WebAuthn Device Biometrics as a first factor is not supported for Passwordless connections, and is only tied to database connections. Configure WebAuthn with Device Biometrics for Passwordless Authentication
If you would like to see this functionality in a future release of Auth0, we would encourage you to submit a feature request using this form: Auth0: Secure access for everyone. But not just anyone.. This is a direct line to our Product team and the best way to communicate your needs.