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Is there no in-game workaround? Seems odd to have to mess with your computers settings instead of doing it inside the game so it'll go back to normal once the game is closed.

Edit: and it seems my monitor can't even switch to anything except 16:10 resolutions at that, weird.

I thought I'd try the old Alt Enter to exit fullscreen trick, but no, the game remains in a 16:10 mode even in windowed. 
Example of sides being cut off below.

So it seems the game doesn't resize well, but Unity also forces it to conform to the native screen format in some ways.