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DiegoRojo i believe we can agree the problem is more complex than reducing it to PWM issues and display type
Oh you don't even imagine how far it is from display type and pwm and things like that. I am doing all the research in another language so there's little of it on this forum right now; but there's a community of people who face this smartphone problem and a lot of tests are already done. For me old Samsung Note 5 (super amoled with low pwm rate) is the last normal phone, and iPhone 11 and Xiaomi with ips bring me a lot of pain immediately.
No recommendations right now, unfortunately. Only one: avoid pushing through pain, bad phone will just damage eyes more and more. If your redmi has something like "reduce contrast" in settings, try it, it is helpful on some devices. Contrast has something to do with this, but not per se, it just messes up some physical qualities of this light.
Ledstrain generally is visited by people with other types of problems, so this smartphone problem is less covered here. But I have to say it is not exclusive on smartphones, it has something to do with the basic screen technologies and eye sensitivity to this specific kind of damage. So some people have the same problem with notebooks, monitors etc. It is definitely most present in new tech (starting from 2017), but could be found earlier sometimes.
It is definitely not connected to any eye pathology, a lot of people I contacted have been to ophthalmologists. Me too, I had a complete checkup with a lot of tests and my eyes are absolutely healthy.
Neither it is connected with BVD, discussed here; most probably this light makes eyes to immediately excessively converge reflectively. But that is only a top of an iceberg; somehow it makes little red blood vessels to appear or break immediately, leads to light sensitivity (hopefully by damaging only cornea and not a retina, but it is impossible to define) and so on. The longer it is used, the more damage a person feels, but muscle pain from excessive convergence will slowly go down.