You will not get burn in for long gaming sessions. That sort of thing is called image retention. The easiest way to think about this whole thing is that each pixel is organic. Being that it is organic, the pixel has a certain lifespan. When a static image is on the screen, the pixels are essentially burning their life away to produce the image. As the pixels burn down, you will start to notice an unevenness to the colors on the screen. This is because the pixel has exhausted a certain amount of its life displaying a certain color. That being said, gaming on the screen will eventually turn into a burnt in image, but that take many, many hours. The half-life of most OLED panels is something near 100,000 hours.
Check out this page from Rtings: https://www.rtings.com/tv/learn/real-life-oled-burn-in-test
It should do a better job of explaining image retention and burn in.