Well, if you did clean Win install, and not just reset (by clean, i mean format OS drive, make new Win installation), then this gets rid of all software issues, like bloatware and malware (except firmware rootkits). With this, it is safe to assume that software works fine and issue is with hardware.
Well, to fix it yourself, without monitor RMA, you need to replace the monitor panel.
Meaning complete disassemble the monitor, procure 2nd correct panel and replacing the panel. But this will void the warranty your monitor has. And also needs in-depth know-how of monitors. Maybe even requires soldering, depending on how the panel ribbon cable is connected to the monitor PCB.
Here's video of monitor panel replacement:
But do note, that monitor disassembly is different for each and every monitor.
View: https://www.youtube.com/watch?v=a0V22GptM44
This is a better image and i take you took it with your phone? Since there, i can see vertical green line and horizontal blue line. Indicating impact to the monitor panel. Or could be just LED failure inside the panel itself.