Displays turns always on automaticly (during screen lock)

Hi,
I set up zorin core 16.1 a few days ago on a new PC. It's an intel nuc 11. Zorin works fine, but I have a problem as soon as I lock my screens (Ctrl + L) : after only a few seconds, the screens turns on again, then turns off and on again and again in a loop. Finally, my screens nevers really stop.

The installation is new, I did not install any screensaver-like package. No such option enabled.
I tried to disable notifications on the lockscreen: it works, but does not solve my problem. I tried disabling WIFI and prefer ethernet. I turned off bluetooth. Night light is disabled. Tried unplug usb keyboard/mouse/soundbar just in case. I also tried to change the (new) HDMI cables of the screens.

I don't understand why my two HDMI screens always turn back on. I work with another computer, and other screens right next to this one and all day long if I don't turn off the screens, I see them being blank, then turn on again --> slow blanking way (5 to 10 seconds off, then a minute on ... infinite loop until I became epileptic or just nervous ^^ )

On the other hand, it seems that sometimes the screens are black, but not turned off (I still see the cursor).

I'm not the first to have these problems (on other distros):

Do you have an idea how to do it?

Thanks for your help.

Did xset dpms force off not work?

You might try

#!/usr/bin/perl
`gnome-screensaver-command --lock && sleep 5 && xset dpms force off `;

Save that content in a file as screen-off.pl
Give it executable permission:

chmod +x screen-off.pl

Open Settings and navigate to your Keyboard Shorctuts.
Replace the ctrl+alt+L shortcut with the command pointing to the location of that script you saved above.

Thank Aravisian for your help.

First time I execute x xset dpms force off I get :

set: unable to open display ""

For the script you provide, I need to install gnome-screensaver, then the result is not different (does not solve my problem).

But after I have install this package, xset command works ( around 4 seconds before screen turns on again)

Hmmm... Can you please post the output of

xrandr

While all devices / monitors are connected?