How to add face recognition to start iPhone instead entering your code
How to add face recognition instead of using code
iPhone 12, iOS 15
This presumes you did not activate Face Recognition when you set up your iPhone and instead you are using the passcode. Your iPhone 12 is capable of Face Recognition which was introduced with the iPhone X (ie. 10) range in 2017.
To set up Face Recognition follow the steps in this support document.
Start by going to Settings > Face ID & Passcode