Numbers.app, Autodesk Fusion, Adobe Illustrator, and Terminal.app were the first places I noticed it. And in Fusion and Illustrator it's not text that's the issue but lines/graphics.
And high contrast edges in photos in Apple Photos looked wonky.
Oof, at least two of those apps should not do that. I wonder how Fusion and Illustrator do lines, because last time I touched Illustrator (CS6 era), its line drawing was pretty good.
I'd like to see screenshots of these showing off the weirdness, if you don't mind.
I wanted to see what it looked like on my 24" 1080p IPS monitors (two Dell U2414H IPS, and a rebranded LG FastIPS from Monoprice). I don't own a Mac, so I can't replicate it.
All of those share similar traits: the lines are excessively soft in many cases. They're rendered in linear space and then baked to the target gamma ramp, instead of being rendered in sigmoidal space (or some other psudeo-sharpening/pixel-aligning w/o sharpening methodology).
The font in Numbers is extremely misrendered, that's soft even for Core Text standards. Its as if it had absolutely no hinting applied, instead of the kind they use that approximates Freetype's "light" hinting.
The Terminal.app one is okay, but not amazing, as you can see slight misshapen stems, such as in the M for Makefile.
So, I'm not sure the monitor was at fault, but given the "clear and sharp" nature of OLEDs, it certainly magnified the effect.
And high contrast edges in photos in Apple Photos looked wonky.