Edward I've seen a few posts like yours recently. And I feel pretty much the same as I did back in 2012 when this started for me - frustrated, struggling, and not clear on what technologies are even relevant to my situation. Does this sound true: the problem is more complex than our current available means of investigating it. If it is or not, what should we be doing?
I have learned more about displays and graphics in the last 5 years thanks to this site and others than ever before. I share your frustrations, however. Everything in my gut tells me that temporal dithering is the issue for most people here. PWM is very easy to rule out (simply don't use a screen that uses PWM!) but then it gets more complicated with pixel inversion (at this point my knowledge runs out).
If I have a good device and a bad device using the same HDMI cable and the same monitor, then the techie in me says "OK, it's something to do with the hardware/software in this machine" (monitor has been ruled out as the cause). So at this point we're looking at the 'point of failure' being..
VBIOS (Mobo/GPU) (which may default to temporal dither, hence why even on POST screens we get discomfort on new tech)
OS itself (W10 composition spaces).
OS Drivers (which could be set to temporal dither)
VBIOS is locked down and generally unaccessible to make changes AFAIK
OS - Maybe a regedit or fix could disable any OS tomfoolery
OS Drivers - (Ditherig/Nvidia reg keys which aren't 100%).
Reading into the patents concerning Temporal Dithering have been somewhat revealatory to me. It does cause flicker, regardless of how miniscule it's claimed to be or how it can "fool the eyes" to see the extra colors. It is snake oil for supposed '10 bit' displays, which in fact are 8bit. Or it's to guarantee uniformity of color on any panel. Which makes sense from a customer satisfaction perspective, but flicker is flicker.