To solve the flickering, in KDE Plasma, set the game to window mode, match your screen resolution, center the window in your screen, then right-click on the title bar, disable the title bar and frame in the "More" section, right-click on the game icon in the taskbar, and check "Keep Above Others". Next time you launch the game, change the resolution to something else, then change it back to what it was previously, and repeat the earlier steps.