Hello there,
Thanks for reaching to the Microsoft Community. If your Surface camera isn’t working at login, check if Windows Hello Face is set up in Settings > Accounts > Sign-in options. If it’s missing or says unavailable, try opening the Camera app to see if the camera works. If not, update or reinstall the camera driver via Device Manager, and make sure Windows is fully updated.
Let me know your Surface model and Windows version if it still doesn’t work.
All the best.