First thing you should do is run a screen diagnostic.  Hold D through powerup.  Does the same fault appear on the test screen?

You have to perform the ‘LCD BIST’ (Built in Self-test) on the computer. Please follow the steps mentioned below to run the “LCD BIST’.

1. Turn of the computer.
2. Press and hold down the ‘D’ key on the keyboard and press the Power button.
3. You will see different colors on the LCD screen. Please check if the issue reoccurs on the screen.

In addition, please connect the system to an external monitor and check if the issue reoccurs.

@ejn63​ Almost similar issue with my inspiron, holding up D, there is no problem with RGB. When I connected to external display via HDMI, these are not appearing