It’s called side loading for a reason
https://play.google.com/store/apps/details?id=com.googlecode.eyesfree.setorientation&hl=en
I forgot the exact apps name but you can find it in the play store. IIRC the app will auto start and force the orientation to landscape
I would love to see the Xbox app actually released for Android TV with Remote Play enabled.
My thought was the Xbox app looks similar to windows 10. Which has display options so you can orient your screen horizontally (like you would normally use it) or vertically like your showing to read long documents. I’ve seen some lawyers set their computers up to read long documents without scrolling.
So within the app. Look for display settings.
Try typing display, then look for advanced display options and set to horizontal.
How does the app look? Can you get it to do 4k? Could save me moving my Xbox around the house.
Flip your TV