Hello sn_695,
As Neel Malik was saying with Windows Hello set up it is already configured to scan for your face every time you sign in/open the lid. Most likely the process is happening so quickly you feel like it's not actually scanning. The reason the Require Sign In option is grayed out is because it's unnecessary with Hello enabled, it's already doing it.
To rule out any possible conflicts or issues Kimberly__L asked the status of those settings & options; but they do not need to be changed for Windows Hello. Installing Windows Updates with a new device and making sure your account is verified can ensure that everything is working properly and as it should be.
Tabi
Surface Technical Team