Cool. Yes, the 3 arrows are pointing to the edge of my screen protector. I do not think that adding a layer will help. The surface of Librem 5 (without a cover) covers the lens, so it is flush with everything except for where the speaker is. The glass sticks out from the frame, which I suppose is easier to build and looks nice, but is less protective of the glass.
I was looking into how touch screens work because someone mentioned that it was not RF (radio frequency) energy. They are correct, but there are charges being produced. It is just not high enough in frequency to be considered RF. Exceptionally dry skin, such as calluses would make it difficult to detect a touch, but I am not sure it would produce what you are seeing. RF, however, can interfere with touch screens. One source could be the charger that a phone is plugged into, or some kind of transmitter that is near by, like a WiFi access point. Does this only happen on a charger? Does it change behavior in another room or building? It is possible that the touch screen interference can be coming from within the phone. Maybe try turning the top 2 kill switches in the down position to check the cell and WiFi cards. It could still be coming from the mainboard though.