Wait... so operating at 100% brightness mitigates this? I bought this mac and have been reading about this. Stare at computer 15+ hours a day coding, but I also never use anything less than 100% brightness.
PWM is usually only used for dimming. So at 100% brightness there is no PWM being used. I'm not sure how this apple monitor works, but that's the basic gist for most screens that use PWM for dimming.
If you have a modern-ish phone to go with that Mac, try taking a slo-mo video of your screen (preferably with content with decent sized patches of something other than black or dark gray) at different brightness settings. Maybe even make a big gradient and display that at various brightness settings.