a problem was detected with the truedepth camera. face id has been disabled

if it was me then I would take a backup

and then try to restore it to factory settings Restore your iPhone, iPad, or iPod to factory settings - Apple Support

if it was still a problem then I would expect it to require repair to work once more

You should never update to iOS 15 Beta if you aren’t a developer. But you found a bug yaaay.

He should go to apple store to get him repair face id