Usual contenders are:
Lighting:
* Exposed lighting strip in wooden (often striped) background - they hurt me to look at and are often placed in eyelines.
* Exposed bulbs in whatever fancy arrangement. (Faux 40s ones often flicker).
* Spotlights which are too dispersed so there's point sources of pain while it's just too dim overall - usually spotable by shadows. For extra shits and giggles sometimes you end up with multiple shadows from multiple light sources which means I'm getting eye strain from focus issues. Shadow is often a warning sign for me.
* Reflections of light sources on too much glass or glossy surfaces - I can't tell what's real and what's reflection and my brain goes into panic.
* Just TOO damned bright overall, overlit at 600-800Lux Cos Airy...
Any and often many types of lighting can flicker for various reasons, e.g. wornout CFLs, magnetic ballast fluorescents at end of life and modern LEDs with shit control electronics. I can't tell if flicker exists without either video at 60fps (it beat frequencies with our likely UK 100Hz harmonics) or seeing it for myself. Sometimes if the light is v bright it can be flickering but I can't see it - but still get headaches from hell. I can often SEE the flicker, it makes everything stripy in my vision.
Stripy interiors:
There is a mathematical formula for how "visually stressful" something is, basically closer to the ratio of 3 cycles per degree which is the relative width of stripes to one another... Eyecatching for some, debilitating for others.
I also struggle with aircon grilles which tend to be silver with black holes and they literally vibrate and are unbearable for me to look at.
Often patterns of dots can also be visually stressful, too much visual noise, too much to focus on. Extra lolz if they use strong conflicting colours like blue and red/orange as those bother most people.
Lots of clashingly harsh contrast, so super white walls with often dark or bright red or strong colour interiors. Some contrast good, too much contrast bad. Also when contrast is used for no purpose, so doesn't denote doorways or walking lines, but is just random.
This video covers some of the stripy stuff:
https://www.youtube.com/watch?v=GBOzv9HgoWM And the acoustics of these things are often AWFUL. There's no legal requirements for it.