My issue isn't caused by Windows 10's old DWM, Desktop Window Manager or refresh rate code. Therefore, when WOW Classic TBC Gold WoW was running on my primary monitor would need be synchronized to the level that my GPU could do, and it was generally not quite 144 FPS. It would then run into an issue. My second monitor worked perfectly and was set to the 144hz. The DWM would produce flashing and also drop frames on my primary screen.
Before when I had my primary running at 144hz and my secondary at 60hz I didn't notice because DWM at the time, unnoticed to me it had set both framerates at 60 anyway. It was still happening sometimes, but I realized that any solution to it resulted in my game's FPS decreasing to 60.
The flicker I saw was reproduced in crafting. When I turned leather scraps into leather and noticed a tiny flicker after the job was completed. My mods that I have used are running and I am having no problems.
What does a high-quality PC mean? Which resolution are you using? Do you use gsync or freesync? Do you know the maximum frame rate that your monitor can support? Are you running your monitor at a a high refresh rate? It seems like the issue is in your computer. How much power does your GPU using while playing? What is the one core that will amaze you with the power of your CPU while you play?
Raid was experiencing issues for me for a few weeks. I had been trying out add-ons and had issues. My issue was solved when I disabled Details streaming (I believe that's what it's called, but I'm at home right now) You might try that in case you are also using details.
If you are using Rivatuner try to turn it off. It has caused my game to freeze rather than stabbing, but you don't realize it. I'm using the game's fps cap to avoid this, but unfortunately I also occasionally experience slowing down, I'm thinking it's due to add-ons, and it's significantly more frequent buy WOW TBC Gold when running multiple clients, like every 10-20 seconds.