Windows - AMD Graphics

https://ledstrain.org/d/80
Find your registry path (in Catalyst Control Center, go to preferences->advanced->Information->Software)
Run regedit, browse to that path.

Look for the target key, which is either 0000 or 0001 (or both, if you have enough outputs). Make a new 32-bit DWORD:

DP_DisableDither=1    if you have DisplayPort connection
TMDS_DisableDither=1  if you have DVI connection
HDMI_DisableDither=1  if you have HDMI connection

Reboot.

Windows - nVidia Graphics

https://ledstrain.org/d/511 + https://forums.geforce.com/default/topic/1082681

Windows - Intel Graphics

https://ledstrain.org/d/80
Try ditherig.exe http://kawamoto.no-ip.org/henteko/myapp_en.html

Windows - Microsoft Standard VGA Adapter

No problem.

Linux - Graphics

(leave for history) ref: https://ledstrain.org/d/413/13
(leave for history) ref: https://forums.guru3d.com/threads/how-to-disable-dithering-in-linux.387362
(leave for history) ref: https://nouveau.freedesktop.org/wiki/Dithering
(leave for history) ref: https://help.teradici.com/s/article/1048

Mac OS -

No method, give up.

Leave "Automatically adjust brightness" on.