Given this thread is a bit older, I'm not sure my input will be that useful as you may have already decided, but I thought I'd chime in.
Having owned an OLED (a 2016 LG E6), I won't personally be going that route again and have gone for a Sony LCD instead this time around. I got significant burn-in first noticeable after about 6 months and getting progressively worse as I owned the set. It was not unwatchably bad and only really showed up with certain colors (reds and yellows particularly), but it was most definitely there and quite noticeable in some situations. I was able to find the TV a new home without much trouble though, and the picture was still good when it left me in most situations.
I never abused the set. I did game a good bit on it, though, and some of them were longer games. The worst offender ended up being Zelda: Breath of the Wild, and I ended up playing that game for hundreds of hours total, but only a few hours (usually 3 or less) each session with plenty of different content in between as well as many days I didn't play at all. The upper left hand corner hearts, as well as the orange part of the temperature gauge in the lower right, were the first things I noticed burned into the set. I should note I kept Game mode on default settings as well (it was bright, but not absurdly so). Eventually, I noticed the CNN logo start to burn in as well as a bit of evidence from the ticker (and I do watch a decent amount of CNN, but again, not ridiculous amounts and I never left it there for marathons on end). The burn-in for me seemed completely cumulative instead of from any single abusive session. (I also was miffed because I'd investigated burn-in prior to purchase and was led to believe it would not be an issue.)
I owned a plasma before the OLED, and while I did eventually get a little bit of burn-in there, the OLED definitely burned in faster and seemed more noticeable to me.
Your mileage may vary. I really enjoyed my OLED, but decided I would not be going that route again since I do game and tend to play games for quite a bit of time cumulatively. LG does not cover burn-in, but I believe there ARE warranties through Best Buy that might, so I'd certainly go that route if you do end up going OLED. I was told by the Best Buy guy who delivered my Sony that had I had the Best Buy coverage on the OLED, it would have covered an OLED replacement; if true, that might be an option for you.
This is just my own experience; others game a ton and don't seem to have a problem, and I guess it can even vary by panel how much you get. Just know it can and does happen to some people.