While I use Slackware, and have used KDE before, I have not used this particular aspect of it.
As per the documentation:
https://docs.kde.org/trunk5/en/kde-w...art/index.html
The program scans $HOME/.config/autostart/, $HOME/.config/plasma-workspace/env and $HOME/.config/plasma-workspace/shutdown folders to check what programs and scripts are already there and displays them. It allows you to manage them easily.
So, maybe there's something in these directories?