I have an older Insignia tv and a Roku Ultra 2019. If I select "Normal" from the TV's zoom options, the Roku video input is displayed in 4:3 aspect ratio and it is squished horizontally. If I select "Wide" from the TV's zoom options, the Roku video output is displayed as 16:9 but is also zoomed-in so that a portion of each edge is cut off.
My Xbox One, an old Blu-ray player, and broadcast tv channels do not have this problem. I can set the TV's zoom option to "Normal" and they are all displayed in 16:9.
It seems as if the Roku is not passing something along with it's signal to force 16:9. I have looked to find hidden settings but cannot find anything. I would appreciate any help to get the best picture out of the Roku I can. I got it so I didn't have to rely on the Xbox One for streaming