When playing in 4:3 there is 1 line of pixels that aren’t covered up by the borders in both classic and remastered graphics. It’s not noticeable in the picture but in my setup it’s very distracting in game. Cinematic bars also do not work in 16:9. They work mostly fine in 4:3. In 21:9 bars only show up in classic graphics and cover the left and right parts of the screen.
Make sure and file a bug report about this on the Halo Support site: https://aka.ms/HaloSupport
Be sure to read over the known issues list first before reporting