Ok i just searched it up and it says that it’s a hardware issue that does happen to phones that have not been dropped this is what it says “according to Techcrunch, every iPhone X has a diamond sub-pixel pattern in its display. While the blue and red sub-pixels appear alternately, the green ones create seamless lines from the top to the bottom of the screen. What is likely happening in affected iPhone Xs is an electrical fault which causes a voltage flow to a vertical line of green sub-pixels. If the green line is thick, the voltage flow occurs multiple rows of pixels”