HDMI-CEC really depends on the hardware you are using, and if your graphic card supports HDMI CEC.
If it does, you then need to find a library to send information to that bus and create a custom interface asset to send the commands.
In the signage industry, I heard several times that HDMI CEC isn’t really reliable, and RS232 is preferred. In that case, you can probably re-use this interface asset to send the proper commands to the serial bus, again depending on your hardware (monitor brand / expected commands).