Hi......most monitors seem to be designed to have brightness set up to be normal for most people somewhere around 20%. You should not ordinarily be setting it much higher than that, unless the monitor is particularly old and faded.
It's quite common to set it much dimmer than that, all the way down to 0%. Generally speaking, the darker the room is, the lower the brightness should be set. PWM-free monitors are a good idea if you are working in very dim rooms, because some cheap and irresponsibly designed PWM monitors may have flicker at Hz low enough for those sensitive to flicker to notice when brightness is set that low.
Don't use monitors or TVs in a completely dark room. That's a shortcut to eyestrain. You need a certain minimum of light in the room. Bias lighting, which is simply having a dim light bulb on behind the monitor, is a good idea to mitigate eyestrain.