TrueDepth camera disabled

their page says it's because

1. one replaced it with a non official cam
2. it took damage somehow
3. the component became defect

and

"What to do next

1. Update your iPhone or iPad to the latest version of iOS or iPadOS.
2. Check if there is an issue with Face ID in your iPhone's parts and service history. To do this, open the Settings app, tap General, then tap About.
3. If you still can't enroll your face or unlock your device with Face ID, you can take your device to an Apple Store or Apple Authorized Service Provider, or contact Apple Support about your iPhone or your iPad.

Only a trained technician should service your device. Improper repair, modification, or use of nongenuine Apple components in the laser systems might prevent the safety mechanisms from functioning properly and could cause hazardous exposure and injury to eyes or skin.

"

so if it's under warranty then I would head to Legal - Hardware Warranties - Apple

and or reach out to their support channels

 Get Support (apple.com)

And or

 Contact - Official Apple

Support

And or

Contact - How to Contact Us - Apple

Or

Genius Bar Reservation and Apple

Support Options - Apple

The FaceID camera array is reliant upon several components - including an IR camera and IR dot-projector. If any element of the array is faulty, FaceID will not work.

This iPhone User Guide describes setup and use of FaceID on supported models of iPhone:

Set up Face ID on iPhone - Apple Support

If FaceID isn't working as expected, or has been disabled, you’ll need to follow this guidance:

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

If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support

If you unable to resolve a problem, you would be well advised to seek assistance directly from Apple Support:

Official Apple Support

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your device. If a fault is confirmed, you'll be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple