Interesting. So you are using the XBOX internal app and passing that signal to the TV. Was the flickering similar to what I posted on that YouTube video? If so, that would suggest it's more than just a problem with using only the internal apps and a backlight or dimming zone algorithm problem.Here is another weird one that I encountered last night:
I turned on the MLB app on the Xbox Series X to watch the Giants/Padres game. It hadn't started yet, so I just got a "Game will begin shortly" screen and left it there waiting for the game to start. When it did, it opened with a view of the field from the outfield stands. The screen brightness was flickering in and out, so much so that I initially thought it was a time lapse of the day with the clouds going in and out. Then, it cut to a dugout scene and I could see it was still doing it. After about 10 seconds of me thinking "well this is going to be unwatchable", the whole thing suddenly resolved itself and looked fantastic for the rest of the game. Not a single hiccup after that.
It was like it had to switch a mode for it to work and took some time recognizing and getting there. There are some definite software growing pains going on right now.