Al alim Channel

Whenever i turn my laptop on, after using for 15-20mins/ half an hour the horizontal line on the top of the display showed...

did you turned off the Mac or just the screen ? for me I use an external monitor and I use at the same time SwitchResX to turn off mac's display but when I turn on Mac's screen (retina) I notice the same problem even if all the time I use external monitor .... Update (05/22/2020): After using the bars becomes a Wall !!