Why does fitness+ not support AppleTV, Airplay2, or lightning to HDMI on a LG TV?

I am having trouble seeing the workouts in fitness+. I purchased a LG Tv with Airplay2 and Apple TV so I could have the workout in on multiple screens to better see what to do. When the fitness program starts it blacks out the airplay screen. it does not make sense. Screen mirroring does not work either. Lightning cable to HDMI does not work. This is very frustrating.