Lock screen with Gnome 3 login greeter

[Richard Forst <sterbl.ta@tutanota.com>]

I switched to use i3. So now after the screen goes blank, it won't display greeter asking to login again. I read somewhere else on the internet that gdm3 (I use Debian 11 with kernel 5.10.0-8-amd64) no longer uses screensaver to lock the session. Instead it uses dbus to activate login asking user to enter id, password for login. However I don't find any related solutions that work. The closest one is [1] (sorry it's Ubuntu env not Debian). But executing that command (in [1]), 

    dbus-send --type=method_call \    
            --dest=org.gnome.ScreenSaver \
            /org/gnome/ScreenSaver \
            org.gnome.ScreenSaver.Lock

login screen doesn't come back. So what command should I use so that when the system becomes idle, the login screen will be active? 

I tried configuring gnome-control-center's Privacy > Screen Lock > Automatic Screen Lock set to on (round icon moved to right). And Automatic Screen Lock Delay is set to 30 seconds. However, it's still active (when becoming idle, screen won't be lock with login display). 

What steps should I perform in order to lock the screen with login being displayed? I know there is xscreensaver. But this time I want to use login instead of xscreensaver, which is nice of course. 

Thanks

[1]. https://askubuntu.com/a/983451