Sounds pretty much the same as what happens to me.
I had a 2015 13" MPB with the retina screen, I've had other non-retina Macbooks / MBP in the past without issues.
Within moments of using it I'd get a headache that would last days. My doctor says this is a migraine and its a trigger but what though
Also get exactly the same symptoms from some other hardware, newer stuff gets me badly.
nothing I did fixed the MBP issue, I sold it after a year or so. I tried all sorts of things even changing the operating system for W10 and varios Linux versions, still same. Something at a embedded hardware / software level caused the problem for me but what that exact thing is I dont know. - external screens didnt help either, these are always OK on my good hardware but NOT ok on my bad hardware.
I would pay for a developer to provide an explanation of the cause and solution for this issue (I have tried ditherig on w10 but it does not fix the issue for me yet), I would go as far to say as it is ruining my life and causing me significant distress. Eventually supply of older machines will be gone and I will not be able to work. The migraine that this causes affects me badly in performance.