How do I enable to TrueDepth Camera on my phone?

Did you recently get your device repaired by a non-Apple certified technician? If so, they might not have used genuine Apple parts, which is causing this message to appear.

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. 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.

Using diagnostics available in iOS 14.6 or later, Apple has detected an issue with your TrueDepth camera that might cause it to not function as expected. The TrueDepth camera contains lasers, which might be disabled for safety reasons if the device malfunctions or is damaged. This won't prevent you from using your iPhone or iPad, but until your iPhone or iPad is updated or serviced, you might not be able to use Face ID, Animoji, Memoji, and some other features that use the front camera.

Read the If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support article for more information. Hope you get this resolved soon!