Here’s the details on FlexGate The Design Flaw Behind MacBook Pro’s “Stage Light” Effect and 2018 MacBook Pros Try to Solve Flexgate Without Admitting It Exists
As you can see the issue was strictly within the displays backlight cable,
In your case the issue is within the T-CON board which controls the scan of the image across the LCD panel. Apple had a second issue related to its systems cooling (2016 thru the current 2021 Intel models). Lets take a deeper look at what yours looks like
13” MacBook Pro Fn
13” MacBook Pro TB
So as we can see between the two 13” models Apple thought the lower clocking of the Fn models wouldn’t need as much cooling dropping one fan and cooling fin from the heat sink! While the TDP of the lower clocked CPU’s was lower the amount of margin was reduced too far! So the T-CON board can overheat if you loose the systems cooling as well as push the system too hard so the system can’t cool properly.
Once the display has started to fail the damage is done! The parts are now weaker so when you push your system it can show up more often. I’m suspecting you have a cold solder joint within the T-CON board or a failed capacitor from being cooked. Someone with the deeper micro soldering skills might be able to extend the systems life or I would just replace the display assembly.
The very first action I would do is make sure the system was clean of dust and debris from the fan and the heat sink fins as well as any dust build up on the logic board.
Next I would install a good thermal monitoring app which can also rev up the systems fan more effectively than Apples thermal model. The negative aspect of this is of course the fans noise! But you don’t need to max out the fan and pre-cooling things before you run a heavy process also makes sense!
This is what I use and recommend! TG Pro