I did not restart Mac, so that requirement might have been removed in release version.
I wonder if I can be sure the kext is loaded and active, if it's shown among loaded kexts. I'm unsure because I do not feel much difference yet. For instance, the Safe Boot still looks different.
si_edgey
According to KextViewr info, the kext is third party, but signed (a closed black lock to the left of the kext name)
Yes, it should be loaded.
I guess I need to go for a few days with it.
Just realized I'm working with the text for quite some time and I do not have a feeling of overworked eyes (like sleepy).
Still cannot use the iMac without Gamma Control. The screen is too bright.
si_edgey Sorry to burst your bubble
https://philtechnicalblog.blogspot.com/2013/02/amulets-temporal-dithering-kext-fear-of.html
checking for the presence of Amulet hardware (that's an expensive dongle!);
JTL Sorry to burst your bubble
https://philtechnicalblog.blogspot.com/2013/02/amulets-temporal-dithering-kext-fear-of.html
On the contrary, this is actually great news because now we know who developed the KEXT. I have tracked him down and am making contact to propose the development of a KEXT for us. I will post updates here as we go on.
tfouto Sorry for my ignorance. What is KEXT?
Google is your friend. 
si_edgey On the contrary, this is actually great news because now we know who developed the KEXT. I have tracked him down and am making contact to propose the development of a KEXT for us. I will post updates here as we go on.
Another one of the articles on that site is interesting, albeit from 2012..
Flailing around the web revealed someone at Disney who has produced tweaks to X's configuration file for use under Linux; unfortunately this doesn't work in OS-X as the dithering is done by the driver.
It's probably way out of date but is very interesting to know how even people in the creative industry for huge corporations have needs to disable dithering.
Well, as said above, the kext might not do its work, although it loads.
After three full days of testing, I can say that I got as tired as before. The same feeling of overworked eyes and head/eye strain/pressure. And I'm pretty sure it's the iMac screen, because I managed to relax somewhat by playing on the iPad 
This only shows itself after prolonged periods of intensive work, so I can spend 1-2 hours at the screen quite easily.
In the process, I also switched off Gamma Control for a while and returned from HD-709 color profile to the standard iMac profile, and after a short time my eyes started burning. This makes me believe that apart from macOS dithering, the iMac screen has brightness issues.
annv After three full days of testing, I can say that I got as tired as before. The same feeling of overworked eyes and head/eye strain/pressure.
Ahh thanks for testing @annv, I'm hoping that the kext will lead us to further developments down the line so it's not the end of the world. I'm hoping to have some more news about it soon.
The developer of the kext to disable temporal dithering on MacOS sent me a very interesting reply. Sadly he does not have the time to be able to work with us on this, but he has given some interesting pointers on how we could proceed with another developer, with the caveat that Apple are moving changing kext's to exist more into the userspace than the kernel as has been mentioned above.
Crucially, they were only able to develop the kext because of a tight relationship between the company he was working for and ATI/AMD, who guided them on how to tweak the right parameters to disable the dithering. They didn't speak to Apple at all, this was done entirely with ATI/AMD as temporal dithering exists at the GPU driver level in MacOS - it's an abstraction the kernel has no interest in handling directly, it just tells the GPU/driver what colour it was where in the framebuffer
There is a hardware check as a 'dongle' for the kext. This could be bypassed by patching the kext to USB vendor ID that the kext looks for to verify hardware. I think this is where we should focus our attention as once bypassed it will at the very least allow us to rule out temporal dithering as the root cause of our issue in MacOS.
If anyone feels like they can do this or knows someone who can then get in touch and I will forward on everything that was said. Failing that we can crowdfund the development cost from this forum I'm sure.
annv
Just a couple of questions if I may:
When you say "HD-709 color profile" which profile are you referring to, and how did you get it?
In Display I have a profile mentioning 709 which is pre-loaded (BT.709-5, spec version 4.0.0) which is just terrible, and I managed to find v2.0.0 of BT.709 from color.org. The latter is much better, everything is pretty much washed out and the screen is a joy to look at compared to the standard iMac profile. The screen is now much more similar to Safe Mode, and when trying to go back to the iMac profile I realise how offensive on the eye that profile is. If anything, BT.709 v2.0.0 is just a bit too much on the pinkey side.
When you say "Gamma Control" are you talking about the app available on the app store for 26 dollar?
Thanks
I have downloaded the HD-709 profile here: https://www.youtube.com/watch?v=YwjLuUR51gE
There is a link under the video.
There is also a description of what it does on the website: https://www.sebastianleitner.com As this person says: go to "DCP Course and ebook". He also says that it's the only profile that does not go through ColorSync utility. He is a video producer and this is the way he makes all the video editing programs on Mac to show the same colors.
I've put it more in detail in this thread: https://ledstrain.org/d/768-colorsync-on-macos-what-is-this-could-it-be-a-culprit
Yes, Gamma Control is the app on the App Store by Michel Fortin, but it costs USD 18.99 in my country. I've bought it from the developer directly on his website though: https://michelf.ca/projects/gamma-control/ This way, it has a trial period and (AFAIR) a better upgrade policy.