The xfce4-screensaver starts even if you have disabled screensaver in "Session and Startup"

xfce4-screensaver 0.1.10, xfce4-session 4.14.2

This is against Freedesktop specification: https://specifications.freedesktop.org/autostart-spec/latest/ar01s02.html

Workaround: uninstall xfce4-screensaver