I've suffered like so many of you with this "invisible" issue and this has effected so many bits of tech that i have bought in the past since i was about 20 and now i'm the ripe old age of 46. I've had issues with TVs, laptops and smart phones. I've tried to narrow it down to what the cause is and come to some conclusions that have worked for me. I don't think its just one thing but i do believe that one aspect is the main factor and that is CONTRAST RATIO of the screen. I find that any screen that has a contrast ratio of over 1000:1 gives me eye strain within minutes. I've tried to "push" through it to the extent that my eyes physically watering but it doesn't get any better the more i persevere. I'm still not sure if PWM is the cause as i've had TVs with zero PWM and my eyes still feel like they are being pinched at each side.
This is my list:-
Tech that doesn't work for me
Samsung s7, s8,
Huawei P9, P20, P20 pro, P10 lite
Google Pixel 2XL
Median Erazer x6000 series
Tech that does work
Hisense 7120 Roku TV
Samsung s2, s4, s6
HTC one m7
Huawei P9 lite, Mate 20 lite
Acer Nitro black edition v15
I also find HTC vive ok and i currently have an Oculus quest which is fine but both do cause a little strain after a few hours but no eye pinching.
Other factors are reflective glass screens don't help and i don't know why but TVs with 120hz panels give me pain so cheaper TVs are more comfortable for me. It also isn't a case of just turning down the contrast on TVs as some manufacturers don't implement this successfully.Also turning artificial sharpness down helps.
Please use the Notebookcheck website for detailed reviews as they measure the Contrast ratio for phones and laptops. Also rtings is great for TV reviews with contrast ratio measurements.
I currently use an HONOR 20 mobile phone with a contrast ratio of 875:1 and i can stare at it all day long if needed.
I don't know why the samsung s2 and s6 were great to use as they are amoled and should have infinite contrast ratio.
Hope this helps others and send me any questions you have.