Option --replace suggests that xfwm4 is replacing another window manager
Option would be needed to run xfwm4 on another DE (e.g. replacing sddm on Manjaro KDE)
But not needed if xfwm4 is default window manager
$ xfconf-query -c xfce4-session -p /sessions/Failsafe/Client0_Command Value is an array with 1 items: xfwm4