When capturing selfies using the True Depth camera with depth data enabled, but without Matte Effects enabled, the nose of the subject is specifically being flattened. It does not matter where in the image the face is, or the angle of the face. The nose is targetted and the depth data is all set to the set value. How much of the nose that gets flattened is related to its distance from the camera.
I have tried several other apps that use the true depth camera and they all seem to produce this result.
This happens on iOS 12+ on both the X and the XS. It did not happen in the past.