I'm trying to turn the monitor off via my RPI, which works good with any of these options
vcgencmd display_power 0
tvservice --off
But then, with both of them, it shows a default message saying something like "Cable not connected". Is there any way to block it or hide it or use any other command that might not end up in the same result?
Instead of turning off, you can go for a blank screensaver
sudo apt install xscreensaver
This provides many options for setting up the screensaver, or disabling it completely.