i think you missed something. when scanlines are applied , press escape to be back to the GUI. Or you can bind another key instead escape. this will stop the effect and you'll see the GUI back. (see the picture below) you should check full tutorial we made on youtube. come on discord if needed
Also we did shortcuts to change effect directly when the overlay is actived. just look for "DEFAULT SHORTCUTS.jpg" inside s4w folder. you also can rebind these shortcuts if needed.
Hope that will help :)