Keep in mind that this is just my personal theory, but it‘s the closest I’ve come to any kind of answer. I found a good general explanation of what temporal dithering is:This theory seems right to me. I got headaches from the iPhone 11 Pro and from the regular iPhone 11 but the 8 Plus and the new 2020 SE are fine. Where can I learn more about dithering?
Temporal dithering (FRC – Frame Rate Control)
FRC (Frame Rate Control) or temporal dithering, as explored by Lagom, describes rapid alternation between a very slightly lighter and very slightly darker variant of a given shade. This is done where the shade itself can’t be displayed, for example if the monitor does not have the necessary bit-depth to display that shade. The GPU may also add its own dithering stage, so even if a monitor is free from dithering (e.g. ‘true 8-bit’ rather than 6-bit + 2-bit FRC) there may be some dithering visible. It is therefore very difficult to achieve a viewing experience entirely free from dithering, but it’s certainly minimised if the monitor itself doesn’t use dithering. This can be thought of as a form of flickering, although it is very different to the flickering you get from PWM whereby there are extreme brightness changes of the entire backlight. This is a minute luminance change that affects certain shades, so most users will not find this problematic even if they are sensitive to PWM usage. Some users still take issue with dithering usage and prefer that it is taken out of the equation, or at least minimised.