You could sorta kinda claim that most OLED displays are not rectangular [1], since only green is at full resolution, with blue and red being at a partial resolution, by sharing those sub pixels between "logical" pixels.
Note for anyone confused, this is about AMOLED displays commonly used in phones and some OLED laptops from a few years ago.
W-OLED and QD-OLED have unconventional layouts compared to LCDs but every pixel has the complete set of sub pixels (RGB for QD-OLED, RGBW for W-OLED) so it looks more like this:
Just mentioning as while AMOLED phones being the majority of OLED displays seems plausible to me, it's likely not what people in this thread are picturing when they see OLED.
[1] https://www.oled-info.com/gs5-diamond-pixel-architecture-not...