Bought a Hisense U6GR a few days ago, my first experience with a Hisense product. Also getting the same "try restarting your tv" message on my Galaxy s9. Not happy about it but at least I'm apparently not alone.
Just upgraded to Android 12 and same behavior. Between this and Roku losing Youtube and Amazon Prime, I'm done with it. Good thing it's Black Friday soon. I can get a TV that let's me customize the picture with out a terrible app.
I tried using Bluestacks for PC and emulate an android phone but Bluestacks does not support the Roku app yet. The devs said it might be fixed in the future so maybe at some point you will be able to do it from your PC.
Yep. Here are pictures. Going to Expert Picture Settings in the Roku app for my TV will give the error "Operation Error Please restart your TV if issue persists" then go back to the devices menu. As you can imagine, no amount of restarting will fulfill its needs.