The game doesn't play well with ultrawide monitors, unfortunately. It's not a big deal if the game wasn't meant to be played in 21:9... However, instead of leaving black bars to the left and right, the game tries to fill the whole screen, which cuts off a large chunk of the top and bottom of the game.
It's not the end of the world, but if the developer ever feels like coming back to this project, it would be nice to see this issue resolved!