The latest Rtings report highlights two issues, though. One is accelerated burn-in through bright static elements (the CNN logo in the case of Rtings). Actually, the OLED monitors, even the QD-OLED ones did fine there, the panel refresh measures were able to clean any image retention, and only in extreme 5% grey slides were traces of permanent burn-in visible (see the picture below). I'm sure with careful handling like turning down the brightness, hiding icons and taskbar one could mitigate it further.
However, the picture below also highlights the second issue, namely uneven wear from watching content in a different aspect ratio on an ultrawide screen. Here Rtings claims it took only 700 hours for it to become visible. They called it the "reverse burn-in" scenario. The accelerated differential wear is not only because the OLEDs in the centre wear off while the ones on the sides are off but also because the monitor sends more power to them since only part of the screen is lit. I don't know whether LG mitigated this issue on their models (watching 21:9 content on those screens would be the equivalent). In real-world content it's not as visible as in 5% slides obviously, Rtings claims it manifests as, e.g., lifted shadows on the sides when watching a dark scene and it's a kind of "cannot unsee" thing if you notice it.
I guess 700 hours can be both a lot and a little, depending on how many hours of 16:9 content one would watch (1 hour daily equals ~ 2 years, 2 hours ~ 1 year). For this reason, their stance is to recommend the screens only for gaming use, while not when used for other things like productivity. As for mitigation measures, I guess it's not that easy. Apart from the obvious "avoid 16:9 content", one could potentially watch 16:9 in a window. If I remember correctly, that's what
@Silent_Buddha does on his LG OLED when playing 21:9 content. Then again, one could also ignore everything I've just written and just RMA the thing under the 3-year burn-in warranty if the worst happens.
I read that the warranty does not guarantee getting a brand-new unit, though, and you could get a refurb.
Link to the part about monitors: