Why is my true depth camera not working?

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