In this thread it was mentioned how a software could manage single/multiple monitors. I was curious to see how it could be possible to make it work without the tool.
So I made a script that change brightness (VCP 10) of my primary monitor for a few seconds.
To learn about the VCP commands refer to : https://milek7.pl/ddcbacklight/mccs.pdf
Among other commands, you can turn on/off (VCP D6) secondary monitor, change contrast (VCP 12), etc. In the example you can see (and parse) a