Never heard of it, looks like I have to do some research. I cannot give you an answer.
Just a guess: The MX5 and Pro 5 both have an OLED-display with the same brightness level, so there is a chance that the displays are the same.
After quick research: PWM is the method to lower the brightness of an Oled display. At an Oled display the pixel itself produces the light, where at a LCD display the pixels only define the color of the specific pixel, but the light comes from white LEDs.