I saw a post when researching OLED flicker and came across this comment:
OLEDs use PWM to show colour/brightness graduations, so even if the display is at 100% brightness, any pixel that's e.g. 50% gray will be off for 50% of the time.
While I can't pass this as fact, it makes sense and I need considered the brightness using what is essentially temporal dithering to show a specific color.
source: https://arstechnica.com/civis/threads/is-oled-screen-flicker-at-thing.1463525/
This could help explain why some of our brains can't focus on text and maybe the display in general.