In order to use your Fido2 key can be used as a password-less authentication method, you will first need to log in to your X account.When logged in, select the option "More" from the options down the left hand column;

Then select the option "Settings and privacy";

Next select "Security and account access", and "Security";

In order to add a Fido key as an authentication method we now need to select "Two-factor authentication";

We must now select the option "Security key";

The following window will now open;

click
, and an email will now be sent to your email address (example below);

At the prompt "Enter the verification code", copy the 6 digit code then click
;

You will now be presented with a screen similar to the one below, click
;

Select the option "Security Key", then click
;

You are now notified that access to google will be prepared with your Fido2 security key - click
to proceed to the next step;

You will be asked to touch the button on your key (if your model has a fingerprint reader you may be asked to provide a finger swipe instead);

Provided you press the button on the Fido2 key in the allowed time, the passkey details will be stored on your Fido2 key, and you will be presented with the following confirmation, click "OK";

X will now ask you final permission to use the security key as an alternative authentication method, click
,

You will now have the opportunity to provide your security key with a suitable name;

At the prompt "Security key name", supply a name of your choice, then click
, and the key will be available to use when you next log in.