My Face ID not working on my iPhone XS Max

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

Note that if the earlier steps do not resolve your issue, step 9 involves contacting Apple support to have your device serviced.

Follow these steps, testing after each step:

• Face ID not working.
• Software Update.
• Turn iPhone on or off.
• Force Restart iPhone.

If that didn’t work, then it could be a hardware issue.

According to Apple:

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.

As a result, I recommend service.

Service Checklist:

• iPhone service pricing.
• Check AppleCare Coverage.
• Get your iPhone ready for service.

Click ▶︎ Start a Repair Request.

Need more help?

• Call 1-800-APLCARE.
• Contact Support.
• iPhone Support.

Click ▶︎ Check Repair Status. 🔧

Good luck! 👋🏼😉

Did someone service the phone at some point and installed non-Apple parts. That can cause FaceID to fail.

Based on other reports here, Apple may elect not to service a device after a non-Apple service provider has been inside.