Now I have done 3 consecutive days of work on my 2018 15"MBP with the following settings:
Color profile: AdobeRGB1998, NightShift: ON-first setting, Screen brightness at 100%, That brightness software-lowered with Iris brightness settings (all other settings untouched).
Oh and taped over the keyboard-screen-strip-thingy as well so it wouldn't be a factor.
Worked with resource-light apps, vscode and such (so that the added ATI graphics would'nt start up) and I can almost say that right now its usable. Can't say that my eyes are totally relaxed, but its manageable - and doing code work has always been more stressful for my eyes.
The ATI radeon Pro 555X is still a partystopper though (nerveous system strain can be felt within 15 minutes of use) and it kicks in every time something resource heavy is run so I can't use any of the adobe design programs or online apps that hardware-accelerate like Figma.
Also official apple accessibility support (not the regular support) actually wrote me back and suggested to run the screen at max brightness and disable all the true tones and night-sifts and such. But night shift is somehow a helping factor as it prevents the integrated intel UHD graphics from dithering that hard.
Cheers to you all and Merry Holidays 🙂