Theatre Mode on Vertical Monitors
On a vertical monitor browser, theatre mode with chat on should fill the horizontal portion of the screen, shifting the chat downwards to fill the bottom right of the screen, similar to how YouTube's theatre mode fill the top portion of vertical monitor, shifting suggested videos on the right downwards. This will increase video screen estate to make it easier to view the videos.
Yes please, it's 2022 and this should've been implemented at this point.
Theatre mode on a portrait monitor should default to putting the chat below the video. This does happen but in order to get it to work the window needs to be expanded past the bounds of the portrait monitor, chat expanded and then fullscreened again. Without doing so Theatre mode does the same thing as fullscreen.