Awesome game! Have you thought about selling the game in Steam? Just like if it was another donation option, it's also possible to reach far more people that way
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Also the game objects (you, the enemies, projectiles, the windows themself) do not scale with resolution, which makes the gameplay area scale with resolution, so playing in a 4K screen makes it huge making bosses that move far more difficult as you have to move a lot more. I suppose that playing at 720p would also change the area and would make it smaller, also affecting difficulty.