I have one of the older, 3rd generation Apple TV boxes, (the sort that came with a clicky remote, not a swipey one). I regularly use it to watch movies and TV shows served up by a Mac currently running High Sierra (I think… might be Mojave), via iTunes with home sharing.
Given that iTunes is a thing of the past in Catalina, will this set up still work if I upgrade the Mac to MacOS 10.15?