I have a 2017 LG OLED B7 and after a couple of years it got screen burn. It had a square in the middle of the panel as well as the netflix logo. You can run the screen burn tests on Youtube to see if you have any.
LG replaced the screen for free last week. In this particular model, the screen burn issue was a defect in the panel and LG will replace it free of charge. I was lucky enough to get a much newer panel than the one that was originally in the TV, the picture is amazing now!
Best way to avoid screen burn is to keep the OLED Light settings less than 50, ideally around 25 - 40 and obviously use the screen saver and not leave static images / pictures on the screen for very long periods of time.