[RajBhai]

I've long thought that U2F should be incorporated into phones, since everyone has one of those. Even not well off people in third world countries. In order for U2F to proliferate, everyone should have access to it. A $10 FIDO key probably won't be given a consideration if they think a free password is good enough.

[tialaramex]

WebAuthn is the modern replacement for U2F. Do not deploy greenfield U2F, it's a legacy technology only.

A modern iPhone or high-end Android phone already does WebAuthn secured with your fingerprint or (on some iPhone models) facial recognition, like your lock screen or contactless payments.