NewDwarf Set the wallpaper to Stone (solid color preset), either Color LCD or sRGB profile, no True Tone or Night Shift, use max brightness, and measure again.
It's also not just a problem with the wallpaper system, because taking a screenshot of the Stone wallpaper and opening it in Preview or a web browser also caused the same exact flickering on camera.
Flickering was caught on camera displaying this color on both of my M2 Air test devices (which by the way, actually had totally different panels with very different looking antireflective coatings and color tints!) — flicker was clearly visible in 240hz slow motion no matter if Stillcolor was disabled or enabled.
No lights were on in the room.
In comparison, this flicker did not occur at all on the M2 Touch Bar Pro, I even took a recording of the Touch Bar Pro and the two Airs all side-by-side to verify this. Both Airs flickered, and the Touch Bar Pro didn't!
(Aside from the OLED touch bar strip flickering, obviously. I tested with the Touch Bar turned off to eliminate this from the comparison.)
I do not think it is dithering because dithering can almost never be captured on camera. Even in extreme cases like monitors with really terrible and noticeable FRC that I can visibly see flicker through my eyes, it's still too fine for cameras to usually be able to see it.
