Almost looks like it is outputting SBS 3d video output. (side by side)
Is that an external input? I had a similar issue with my roku stick and changing to Sonys enhanced input. Ultimately, I moved to a different hdmi connection. Some details about the set and if this is external or internal might help.
I bought a TV one time and when I got it home it was just like this this was years ago I still have the TV don’t remember how I got it back to single screen but it was in settings of a TV back down I didn’t have a card to buy suck up to it helps this helps btw I remember thinking it was on split screen, like a computer monitor or something.
First: full reboot.
Some context -
This is MI TV 50 4X, Android TV
Is developer options enabled? If so then disable it and reboot device.
Turn off 3D settings. Some TV has it.