My desktop resolution is 3440x1440, but setting the game to that resolution has the top and bottom of the screen cut off (I can only see the very top of the Setting button, for example, the rest is off-screen). This happens both in the browser game and the downloaded game, on Full Screen, Full Screen Windowed, and Maximized Windowed.
When setting the game to 2560x1440, however, the game displays fine (although black bars on the sides, since it's not a 21:9 resolution).
I assume this means, even though the resolutions are in the settings, this game doesn't actually support ultrawide desktops?