ARC should work with in built apps too.
Have you got HDMI CEC turned on?
Edit: 3 Handshake/Conversation issues abound!
I thought that somehow HDR might get affected/turned off/not be detected, and it did momentarily: I had to turn HDR off then on again in the Options for FFXV, but the moment it turned on and I was leaving then menu, the "An HDR video is playing" banner dropped down. Gonna test grand tour in the TV Amazon app for HDR handshake crap....
Edit 2: I ran a cable out from HDMI 2 from my reciever to the HDMI 1 on the Connect Box, and added another cable from HDMI 1 Out (ARC) on the reciever to HDMI 4 In (ARC) on the CB, and sound still was not coming out from the apps nor was video showing up for the PS4 Pro.....
.......then, while reading online about how to fix this for like 10-15 minutes.... all of a sudden from seemingly nowhere without pressing any buttons, the picture shows up for the PS4 Pro with sound, I test all my inputs on the reciever, and all devices output audio (4K BD player, etc)... so I try the Amazon app (have sound set to 7 Ch Stereo), push play on a Pokémon episode to test for sound, and voila! I have sound and picture on all devices out of the blue!
I read that ARC/CEC don't have any standards and that it can hit or miss with how the devices talk to each other. Well, I guess my devices need to have a longer than normal conversation, because I can explain what happened.
Edit: Looks like I do need CEC on, but I still can't get it to work.
Any of you guys or gals mind sharing how you have your TV set to output audio from its built in apps to a receiver, so that I could mimic those settings?!
No, mine is off, and I didn't think you'd need that on for the ARC to work.