Everything about starting a xfce4 session is defined in /etc/xdg/xfce4/xinitrc
If you need to disable the xfce4 xscreensaver is better if you just change the global xfce4 property that is called “/startup/screensaver/enabled”.
In case that this property is not already defined is best to use -n (create) option and then we must also provice the -t (type) for that new property (which will be bool).
/usr/bin/xfconf-query -c xfce4-session -n -t bool -p /startup/screensaver/enabled -s false

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