Dark spot on my TV

Hello,

For several weeks now, I have had a dark spot on the left side of my LCD screen (a 5-6 year old LG) on certain colors. I first discovered the problem while watching the movie Wonder Woman, during the scene with the mustard gas and the orange smoke flooding the screen. At first, I thought it was dirt, like grease, but no, for now the mark isn’t too intrusive; with dark colors it isn’t really noticeable, but it’s annoying when there are bright colors or even white (especially for ads like yogurt, which use a lot of white background). I read online that there are many problems of this type with LCDs, especially "clouding" or "banding." If the problem stays the same, it's not too bothersome, but I'm worried that it might get worse, especially since it's no longer under warranty: S

What do you think the issue is?

Here is a photo with the same type of stain: https://image.noelshack.com/fichiers/2017/48/1/1511780066-dsc02120.jpg