How do I set ATV 4K to use 16x9 and not insert black bars above and below the picture
I have a new Sony Bravia XR-50X90J UHD 4K television connected to an Apple TV 4K. When I go to play a movie from, say, Netflix or HBO, it is displayed with black bars above and below the image. This is true even if the movie I'm watching isn't one designed for a theatre screen. Normal OTA TV or content from YouTube TV displays correctly in 16x9. In addition, the ATV desktop and other apps display correctly as well, e.g., they fill the screen.
The Display and Sound/Screen settings on the Sony are grayed out and cannot be changed. I've contacted Sony to try and see how to correct this, but they're saying that it's a setting on ATV that controls this, and for the life of me, I don't see it.
Can anyone give me some direction on how to fix this? I love the new TV and have been using ATV for the last few years on a Samsung 1080 TV and never encountered this problem.
In advance, many thanks for any help offered!