21:9 monitor has 4 side letterboxing for some content?

I recently bought a 21:9 monitor (2560x1080). With some content (movies on Disney+ and Amazon Prime), when i click the fullscreen icon, the content fills the screen. If the content isn’t 21:9, i get 2 sides letterboxing. With some other content (Marvel series on Disney+ and some series on Amazon Prime), when i click the fullscreen icon, i get 4 sides of letterboxing. Does anyone know why or if there’s anything i can do about it?

most content is either 4:3 (Old crt tvs) or 16:9 (letterbox) and 16:10 (Widescreen). Depending on your display’s resolution you may get black boxes if it doesn’t match up.

see if there is a zoom feature on the display.

I’m familiar with letterboxing on the sides when narrower content goes fullscreen. What I’m not familiar with is content that also leaves black boxes on the top and bottom in fullscreen mode. That’s precisely NOT fullscreen.

I contacted Disney+ about this and they told me it’s a known bug that’s being worked on.

I’ll check the monitor for a zoom feature. Thanks.

It seems it’s an issue with the content because season 2 of the show i was watching goes to fullscreen correctly.