The weird jittery / flickering display that “was” happening on my 11 Pro Max was not just a normal OLED screen diff vs other display types. My Xs Max was OLED it never showed that phenomenon.
What I saw, definitely looked like a defect of some sort - either hardware or software.
I figured I would be returning my phone.
At first, I saw it while looking at and scrolling through pictures and while images were displayed in Safari. Both were an unpleasant distortion / vibration of the image.
I had saved a Screen Recording that showed the issue well, but I must have deleted that.
I saw where someone said to turn off View Full HDR images (under Settings / Photos), so I did that and that seemed to help with viewing pics, but I still had the issue with Safari.
I solved that by buying Ad Block Pro. No ad images being displayed, so no more jittery display.
I have also reset phone and installed new SW along the way now and I turned View Full HDR images back on now as a test and the jittery image viewing did nor come back.