I just had a glance at your laptop screens and I can say with certainty it is very likely to be using PWM.
If you hadn't ignored what hayder1983 has said (asking others for validation while conveniently skipping comments that do not align with your confirmation bias) and insisted it is temporal dithering, you wouldn't have put yourself on a wild goose chase.
It has been over 7 months and you probably still havn't had a clue whats going on.
The Modulation of 0.85% may still be quite high (for you) if your PWM is only 500 hertz or below low.
Your slow-motion camera of 240fps or 480fps is not gonna help you to detect if it is really 500 hertz. You'll need to use your manual camera app and switch shutter speed to 1/8000 per second to detect for line artifact.
At least from that you'll know there is PWM below 3860 hertz / no PWM/ or if PWM exist it still ~ is above 3860 hertz at that brightness measured.
Cheers