From what I have heard this is a problem with OLED panels.

I frequently use apps with "night" theme (black background, white UI controls). You know how Android apps have "back" button on the top-left corner, right?

There is also a navbar (back/home/recent buttons). In my case it's a white-ish rectangle that's almost always present on screen. By the time Samsung added an option to hide it, the damage was already done.

I have them both burnt in on my screen. I first noticed them after merely 1.5 years of using the phone.

OLED burn in is a 100% real thing.

Make an image of the back button, revert the color, and make your phone display it when you sleep. You will burn the other pixels and won't see the pattern anymore !

Doesn't this level of "burn in" mean that these oled screens will simply burn-out with use rather quickly?

I've been using OLED for a long time now, and never had this OLED burn in - including one particular phone (Ativ S, so Samsung S3 screen) that was in use by me for years and then used as a navigation system by my mother until the battery perished. However, someone I know had a phone (I believe the Samsung S8) nearly constantly playing videos with full brightness, and there it did show red streaks over the screen. I wonder what kind of usage triggers it.

It does not seem to be a permanent thing though in OLEDs, after some normal usage it recovers perhaps.

I have an early OLED TV that I burned in (left it on for some reason while I was asleep, displaying YouTube). A few years later there is no longer any evidence of the burn-in; it was very apparent at first, but went away quickly with normal use.

The people I know who use waze a lot (30+ min drive to work every day) have the notify icon (bottom right) clearly burned into their OLED phone screens.

As unread this comment on a white background on my phone (Note 8) I can see the burned-in remnants of the keyboard.

LCD can definitely have burn in

My Honor Play phone has this problem if the screen is higher than 50% brightness. It's very bad.