I can't get my Apple TV to stream video via Air Play

With the exception of certain videos, I can't get Air Play to work from my iPhone or iPad to my Apple TV. I've tried restarting, made sure devices are up to date and sharing the same wifi network, restarting devices, etc. I can get audio to show up, but no video.

I've tried Youtube, NFL games and so on. Just audio can be heard. I also tried screen sharing, which works (shows my iPhone screen on the tv) but as soon as I open up an app (ex: NFL game from NFL app) the screen goes black.

Is my older Apple TV not compatible with Air Play? It says it is on Apple documentation. I'm using an Apple TV Model A1469 (3rd generation) and my iPhone is a version 10 and the iPad is about 2 years old. Any ideas? I'm surprised how difficult such a simple functionality is being. Thanks.