Chosen Solution
Make sure you focus in on the Retina series systems when reviewing the answers area as the older Unibody systems used a very different signaling system between the logic board and the display (LVDS signaling) unlike the newer retinal models which use iDP or eDP signaling. While the cable looks the same the signals are very different! Just like how the older analog TV and the newer digital signals are different running down the same Coax cable. Here’s a deeper view on why the change was needed DisplayPort DevCon Presentation iDP So higher resolutions were possible in the display (just like how digital TV also gained from the older analog). So jumping back to your problem what you are seeing on your display will help us understand what is the problem. Update (05/07/2021) This is starting to look like a logic board issue with the GPU. Are you able to connect an external monitor to your system via the Thunderbolt/mini DisplayPort connection? If you can does it too look like this?
