light-locker is no longer supported and can be removed
Xfce 4.20 tour – Screen Locking
There is no dedicated “security” tab anymore. Lock screen management was massively simplified and “Light Locker” was dropped. “lock-on-sleep” is now synchronized with xfce4-session and xfce4-screensaver.Screen locking settings are now only handled by xfce4-screensaver