I have now tested 5 laptops in a few weeks:
Matebook X Pro 2020 - LCD pwm at 60%, used at higher brightness but still caused some eye strain after several hours of use, not usable for work purposes as it would require daily 10 h usage.
Asus Zenbook UX393 - LCD without PWM, but causing much more eye strain than Matebook, probably Temporal dithering?
Dell XPS 9300 - LCD with PWM at 25%, but used at higher brightness, similar to one above, might be a bit less eye strain, but still difficult for work usage
Lenovo Legion 5 Pro - LCD witout PWM, Nvidia 3060 discrete, 165Hz refresh rate. Seems to not cause eye strain, at least not that bad. I have to try it a couple of more days at work. Suspected cause of not causing eye strain is Nvidia discrete graphics and 165 Hz refresh rate.
Asus Zenbook Flip U371 - OLED with PWM below 52 %, 60 Hz slight lowring of brightness above 52%, similar to PWM, but does not seem to cause major eye strain. I will still keep testing.. Suspected reason of not causing eye strain: 10bit OLED without FRC / Temporal dithering and lack of actual PWM above 52%. The slight eye strain that seem to feel might be due to the 60Hz slight banding above 52%, but will it be a problem after using 10h on consecutive days, remains to be seen.
@HAL9000 there are very few actual 10bit screens in the market, none for laptops that I know of. Mostly high end photo editing screens.
I was also able to use CCFL screens with PWM (at least some of those) with minor eye strain. That is because CCFL dims and lights up slowly, so the flicker is not as abrubpt as with LED and OLED.
I personally think that the newer devices are problematic as manufacturers are squeezing more colors out of lower quality panels with Temporal dithring / FRC.
Now why this does not seem to be the case with the Lenovo Nvidia combo is that I disabled the integrated GPU from the bios and use only Nvidia GPU, which might have different type of dithering or no dithering at all. But who knows.
The problem with the non PWM screens causing eye strain is that the eye strain is not immediat like with PWM. it requires several hours of usage. So often times I might think that the screen is OK, but after the second workday where I've used the screen for 8 h or so, I see my eyes being bloodshot. This is similar to CCFL PWM. if ai was gaming every night for several hours, my eyes started to get strained and bloodshot in a couple of days.
This does not happen with my HP ZR40w27 display that does not have PWM. (some 8 years old) or e.g. with Surface Pro 2 at full brighness. Or with Sony televisions without PWM. Even if I would have strained eyes from PWM, I can rest my eyes using the HP display or a sony TV.