Hello STEVERINO,
It looks like iOS has supported this since version 13.3, it’s more about the Operating System rather than the device itself. As iPhone 12 will bur using iOS 13+ you should be able to use the YubiKey5Ci as it supports USB C and Lightning ports.
You can find some more useful information here – https://www.yubico.com/blog/native-support-for-webauthn-and-fido-is-finally-here-on-iphones-and-ipads/
Let me know if that answers your question.