A "clean" reinstall of Xenonauts 2 will often fix the issue if you are experiencing crashes when trying to boot up the game or load a new campaign. These crashes are usually caused by install corruption issues or extra (often old) files floating around which confuse the game and cause it to crash. Uninstalling / reinstalling the game via Steam often will not fix these issues because a Steam uninstall only removes the files it thinks are part of the game, which can leave extra files behind.