Screensaver and Screen-locker
LXQt does not provide its own screensaver or screenlocker but any arbitrary screensaver/locker can be used.
As of July 2021 in order to use the checkbox in LXQt Session Settings, lock actions from the leave-menu or lxqt-runner and lock actions configured in lxqt-config-powermanagement a xdg-screensaver compliant screensaver is needed.
Note that the latter three will install many GTK+ dependencies.
A list of available screen-lockers can be found here.