Users installing Trixie XFCE are running into exactly the issue Ulrich Gaiser describes.
https://forums.debian.net/viewtopic.php?p=827120&hilit=light+locker#p827120 In addition, there is an 11 year old bug in light-locker: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=773743 Users are running into this bug after installing Trixie XFCE https://forums.debian.net/viewtopic.php?p=828455#p828455 xfce4-screensaver does not have this bug: another good reason to remove the light-locker recommend.
