The article actually says so:
>At least two FIDO® Certified* security keys that work with the Apple devices that you use on a regular basis.
>You must add and maintain at least two security keys. You can add up to six keys.
Edit: ok they come in NFC as well. There goes €100...
If cost is a concern, you're buying the wrong keys. You can get FIDO-certified CTAP2 tokens for much less these days (even Yubico's is only about €25 apiece).
The article actually says so:
>At least two FIDO® Certified* security keys that work with the Apple devices that you use on a regular basis.
>You must add and maintain at least two security keys. You can add up to six keys.