That's a good question. It is how you say: Switching to fullscreen doesn't solve the problem. Game keeps the same size, and right side is still cut off. Never saw an issue like yours on itch - seems to be a rare issue. There are options in Unity allowing your game to adjust and scale according to the available space. But I think this isn't a quick fix - might be on option to look for for your next game.
Thanks for trying anyways!