I've a personal smart card with a private key. Is it possible to add as a new authentication method to gmail? It'd be nice to require a card to log in at least in a new device.
Please be aware that Google employees rarely visit this forum, the helpers are all volunteers with experience in Gmail who like assisting other Gmail users.
We cannot know all the details of what will work, so the best advice is to try it and see. Go to the security section of your account an work through the Add a security key steps.
Click on your avatar at the top right of the page
Click on Manage your Google Account
Click on Security
Scroll down to Signing into Google and click on the 2-Step Verification pane
Type in your password to verify access then click on the Security key pane