I just thought I would add my 2p worth to this thread. I have a 2016 LG OLED55E6 which I have had for about 2 years. It was about a year old when I got it. I have been using Netflix for about 18 months and have just noticed that the Netflix logo is visible on a plain red image. This is the red Netflix logo that is visible on the LG Netflix app when you are browsing titles. It can’t be visible on screen for more than 5 or 10 minutes per day, so I think that’s pretty poor. LG make it out that you would need to have static images on screen for hours a day to cause burn-in which is obviously untrue.
Yup it annoys me when you see people give the old "you'll only get burn-in if you leave static images on screen for hours" line. That was with Plasma and those days are gone. It has long been proven that OLED pixel wear is cumulative and that repeated short periods of displaying an image in a certain location on the screen is as bad, if not worse, than leaving a static image there for hours and hours.
By the sounds of it you bought that one 2nd hand so unfortunately that won't be covered by consumer legislation