Upscaling with a receiver
At first I was watching everything through the embedded TV apps, assuming the TV's upscaling was better than that in my receiver (a 2013 Pioneer SC-71 with 4K upscaling and pass-through). I started to compare 1080p Netflix content played with a PS4 and AppleTV running through my receiver with 4K upscaling applied versus 1080p Netflix content through the TV app. Surprisingly, the latter looks much better. When checking the Info with the TV, it indicates that the material coming from the receiver is 4K. And, I really don't see any difference between a 4K program viewed through the TV app and a 1080 version of the program viewed through AppleTV and the receiver.