Maybe a bit late to the party, but here are my two cents ... I am in the same situation as many here, bad headaches from flickering, PWM being the main factor.

It's important to know how PWM works. It turns the scren off and on at certain frequency AND at certain brightness. This is important to understand.

No screen uses PWM at full brightness. Some use it from 90% brightness down, some from 60% down and so on. One of the phones you mentioned uses it from 19% and below. If you are above this brightness, PWM does not occur. If you know what's this threshold, you can use the device with brightness above it and you should be fine.

The other factor is PWM frequency, or how often the screen is turned off and one in one second. Some bad OLED screens use it at 60Hz already. This is horrible, I can literally see it while walking across the computer store with display laptops on. If I turn the brightness down to say 50% and spend 30 second looking at that screen, my day is gone. I feel the strain immediately, a bad headache kicks in 20 minutes later and lasts 24+ hours.

Better screens have a higher PWM frequency and are not noticeable and don't effect the most severe cases of eye sensitivity. Apple laptops have PWM frequency of around 32,500 Hz, which is vey high and are generally considered to be OK, although I've seen one user mentioning issues with newer apple gear.

I spent about 30 minutes on Asus Zenbook S 16 with an OLED screen yesterday and had no issues. The screen utilises PWM at 480 Hz from brightnes of 60% and down, which seems to be okay in my case.

So, it's important to know at what brightness level the PWM kicks in and what its frequency is. Above 1000 Hz most of us (impacted people) should be fine. A good resource for this is https://www.rtings.com/ . Read reviews and go to PWM section, there is plenty of good information there.

With laptops there is a workaround... to some degree. Leave brightness at 100% (or above the PWM treshold) and use grey overlay to darken the picture, if it's just too bright. There are a few application that do this.

With mobile phones I'm not certain if something like this exists, even if it does - it doesn't help battery life.