JTL I don't know how they think it's at 10%. I took photos, and I see the same amount of stripes from 1 until brightness 65. Then at 66 (up to 255) the amount of stripes is reduced to ¼. Which makes sense when they talk about having measured 240 Hz and 60 Hz. But 65/255 is not "10%".
Anyways, I'm using the phone at 68/255 since my last post here and I can use it all day. This is evidence for me that PWM frequency matters a lot. My eyes are slightly red but I don't have strong eye strain or headaches. If I increase the brightness while I'm outside on a sunny day it gets a little uncomfortable though in just a few minutes. So no full recommendation on my end, but I'm glad that I can use an up to date device which is capable of making good photos.
Another thing I noticed is that I quickly get strained eyes when I use "brightness" apps that add an overlay to the screen.
Also anything below brightness 66/255 starts to hurt after a while, makes me both tired and gives me a sensation of facial numbness in no time.
If at one day we could control the PWM frequency it might be a major breakthrough. Then everyone could try and find his own custom frequencies he has no trouble with.
Last but not least, the Developer Options did not help me. I was indeed trying too many things at once, so at first I thought those options helped me while in fact it was the higher brightness levels > 65 and not using "overlay" dimming apps anymore.
Using OxygenOS 's "Night Mode" and sRGB mode also seems to hurt, similar to those overlay apps.