the problem is with the game engine: it's a browser, more or less, and doesn't perform a true fullscreen at all. closest would be a full-sized window mode, with still having all the downsides of window mode (like, less performance than true fullscreen run games).
you can however try and adjust the screen window size by changing the value in the package.json file. be aware there are two of those, one alonsside the game.exe and one inside the www folder. i'm not 100% certain but i'd try to change the line in the file located inside the www folder, i think that should do.
caveat, the game itself might resize the window outline and miss resizing game components along with it, that could lead to displaced items/parts or distorted animations or any other mismatch wherever you go too far out of spec.
i've tried a 720p (that's width 1280 by height 720) setting for one smaller screen and it seemed to work, on a older version.
no guarantees when you try to size for a large resolution.