Issue with screen blanking seems to be affecting older installs that are probably still using light-locker and do not have xfce4-screensaver installed
Xfce 4.20 tour - Screen Locking
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 to avoid conflicts.
A button to open xfce4-screensaver-preferences was added: