Macbook M1 has detectable PWM, Macbook M2 has undetectable PWM, Lenovo ideapad slim 9i don't have PWM, but these laptops all causing eye strain and headache. These laptops also cause you can't sleep at night if you use them before sleep.
It is the IPS screen problem, IPS screen will causing eye strain just because the light it emit is too strong. Because the angle they emitting light, and the area of one pixel is comparatively bigger. IPS screen light didn't be filtered well. Buy a screen filter won't help, it will help a little bit like fifty percent, but won't really solve the problem, I bought a privacy filter which said decrease 96% ultra violet and blue light. It doesn't help much.