I know not everyone is sensitive to it but for the ones who are, it's a major problem. Pain in eyes, headaches, blurry vision, and probably does real damage to the eyes.
I don't know how notebookcheck measures. But, xiaomi lists the display as supporting PWM at 3840hz. Notebookcheck had written 120hz for oneplus 12 but official oneplus also lists a higher PWM frequency than the one measured by notebookcheck.