Maxx do you know about Android eye strain? The tricky situation is that if you don't have both a ROM that is usable and one that introduces eye strain you can't be sure if the flicker that is causing you trouble is the one you see with your camera or the one that comes from Android updating the pixels in a weird way. I have this situation on my OP3. When I use a low brightness, the display hurts because of 240 Hz PWM. But when I use current Android ROMs, it also hurts in the non-PWM range (in a different way, hard to describe). I suspect the bad changes OnePlus has introduced in Android 7.1 for the OP3 are still there for newer devices, too. So your device/ROM probably has them, too.
The same situation happens when we try a new TV. We can't be sure if the (measurable) screen flicker or rather the way the OS updates the pixels is causing our eye strain. Or both of them. It seems OS eye strain and temporal dithering is everywhere on current devices.
And there's also the third issue, white LED in general causing eye strain. You know it when you have to turn the brightness way down on any white LED screen and can't use any LED bulbs, not even those with tiny 0.01% flicker.
I have all 3 types of eye strain and that makes me wonder if they are all based on the same body/health issue. It seems highly unlikely to have 3 different conditions. If it is even correct to speak of "health issues" when there's no trouble at all in natural bright sunlight.