The OLED panel uses pulse width modulation (PWM) to control its brightness. This means that it flickers at a low frequency of 120 Hz across all the brightness levels we measured, which may be problematic for sensitive users.
This means?!
However, the display also works using high-frequency PWM dimming to compensate for the negative effects of PWM flickering. We measured a PWM dimming frequency of 3,846 Hz. How high it should nominally be is not stated in the phone's datasheet.
I don't know either and it's annoying how they can sell mobile phones that may be harmful to our eyes. It's not only xiaomi either, it's almost all manufacturers.