Since the launch of the iPhone XS, there has been criticism of the front-facing camera. In particular, the skin is too soft. This, of course, was called "Beautygate" in connection with Samsung-style beautification filters, which Apple claims are not always used.
In an iPhone XR review, iOS 12.1 told me that it could fix a bug in the Smart HDR camera system and take a more natural picture. Front camera of iPhone XS and XR.
In essence, Smart HDR picked the wrong default frame for HDR processing when it took a self-contained car. Instead of selecting a frame with a shorter shutter speed to stop motion and maintain detail, you sometimes choose a frame with a longer shutter speed. Because the front camera does not have optical image stabilization, blur shots are taken at the same shutter speed as the rear stabilized camera. The result is a loss of detail that looks smooth on the front camera.
For self-portraits, iOS 12.1, which selects the clearest default frame for HDR merging, needs to be modified. I could not test it, but iOS 12.1 is a public beta, so it will be coming soon and everyone will see it soon.