I have a yubikey which supports only U2F. It doesn't support FIDO2. I read about U2F and i understand how it works.
When i test my Yubikey for WebAuthn on https://webauthn.io it works. I wanted to know how WebAuthn works with my Yubikey when there is no support for FIDO2 on my yubikey?
When they say FIDO2 is backward compatible with U2F, does it mean once register my key for FIDO2, it can be used for U2F as well?
If register my key for U2F, can it be used for FIDO2?