glvn Thank you for your response. It took me some time to gather information on devices used.
1) what model of video card and monitor are you using for testing?
In the case of Ditherig + Intel these laptops were used: Dell Latitude E6520, Thinkpad E440, Dynabook Satellite Pro C50-G-113 (all of them posses TN panel, which I also used for testing). Upon enabling Ditherig I could see the effect immediately. I made a picture on how Ditherig works for me with Intel GPU - in the left part Ditherig is not running and in the right part Ditherig is on (banding visible):
With AMD I tried HP 255 G5 laptop with its panel and Viewsonic VA2223-H connected through HDMI or VGA and R.ID drivers and SetupCLI.exe to disable dithering.
I also tried Ditherig with Ryzen 5600G + Dell 2009W.
In both AMD cases I couldn't see a difference.
2) dithering settings made in this way (via the registry) will take effect only after reboot
I tried rebooting both AMD machines and I still didn't see any difference (I expected the same behaviour like with Intel GPUs)..
3) are you using the same monitor for intel graphics and amd graphics?
No, I didn't (most of the devices mentioned don't belong to me; I'm testing whatever is possible to find a new display that would suit my eyes). However, Viewsonic display is mine and I still have Thinkpad with me so I will try and let you know if there is any difference with Ditherig.