That is one of the main problems with OLED technology, it is called BURN IN
I first came across it with a old phone with OLED screen
When I purchased my current LG TV I was very careful to avoid OLED options and chose the NANO technology
18 months in I am still very happy with the screen
No help to you I know, but a warning to future purchasers, of any brand of TV
You could try suing LG on the grounds that the TV is not fit for purpose