PWM is caused when AC voltage is applied to the screen’s light source (e.g. the backlight with LCD, or the screen itself like with OLED). Because the current alternates, flicker is induced, and it can become bothersome at low frequencies (low screen brightness). AFAIK, there is no way around this other than applying DC voltage, regardless of the display technology.
The question is if the manufacturer adds an AC to DC converter. Many monitors now have non-PWM screens, meaning they’re built with DC converters for constant voltage to the backlight. I believe LG’s OLED TVs are also non-PWM. There’s no reason mLED couldn’t be non-PWM, if the manufacturer of the phone, watch, TV etc gave it DC voltage.