Is having two Security Keys mandatory to use as 2FA for Apple ID?

That’s what Apple support says in About Security Keys for Apple ID: “What's required for Security Keys for Apple ID

• At least two FIDO® Certified* security keys that work with the Apple devices that you use on a regular basis.”

I can understand that might be a good practical idea, but mandatory? I’ve only got one. A YubiKey 5Ci so that is made to work on USB-C (MBA M1) and iPhone (13 mini).

I can’t use my 1 security key? Am I going to be required to sign in with both to set up? How does Apple know how many I have?

It’s important to me to use a security key, b/c I am outside of the U.S. a lot and can’t get calls or text with 2FA codes.

Is this some kind of responsibly test, rather than verification? Stunner.

What’s option? Thanks?