Setting up face identification on IPhone 12 Pro

If you're sure that nothing (cover, screen protector, dirt) interferes with your front camera, see this support article:--> If Face ID isn't working on your iPhone or iPad Pro and/or this one:--> If an alert says Face ID has been disabled on your iPhone or iPad Pro

If, after performing all the steps provided in the above support articles, the issue persists, contact Apple Support directly, using this specific link:--> Apple Support , or make an appointment and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple - Find Locations - Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

Did you already force restart your iPhone?

Force restart iPhone - Apple Support

Your TrueDepth camera is not covered by a case or screen protector?

In case you installed the update using your Wi-Fi, try to reset the phone to factory settings on your computer:

Restore your iPhone, iPad or iPod touch to factory settings

Set it up as a new device and see if you can use FaceID.

If this works, restore from the latest backup.

Also check the troubleshooting in this related article:

If Face ID isn't working on your iPhone or iPad Pro - Apple Support