I am trying to add a Yubikey as a security key. I tried with my MacBook Air, and I tried with my iPhone, but the process failed.

I wonder why I can't add my Yubikey as a security key with my Apple ID (on my MacBook Air), since it is FIDO and it also has USB C. I enter the PIN then I'm prompted to enter the PIN again. This doesn't seem right.

When I tried adding the same key with my iPhone it just said I should choose a compatible security key, but this one should be compatible. And it has Fido. So I don't understand what the problem is.