The new "FaceTime Attention Correction" feature, first seen by Mike Rundle on Twitter, can be turned on and off in the FaceTime section of the Settings app, although it only seems to work on iPhone XS and XS Max devices in the third iOS 13 beta sent to developers Tuesday.
Why the feature is limited to these devices remains unknown. Clearly, it depends on some form of image manipulation to achieve its results, so the software algorithms may require more advanced processing power in Apple's latest devices.
In 2017, Rundle predicted that FaceTime Attention Correction would be introduced by Apple in the "coming year", but its apparent involvement in iOS 13 because it was released in the fall has surprised and impressed him .
For more details on the many features that come with iPhones with iOS 13 check out our comprehensive MacRumors roundup.