Have you followed No search results in application launcher - #6 by alkl ?
Make sure that you either restart your system, or restart plasmashell, if you have placed the working org.kde.plasma.kickoff inside ~/.local/share/plasma/plasmoids/:
kquitapp5 plasmashell
kstart5 plasmashell
However, a upstream Bugfix is currently in the state of Merging: Move plasmoid specific properties out of singleton (!744) · Merge requests · Plasma / Plasma Desktop · GitLab and should land inside the next KDE Plasma Release. (I tested it and it seems to work) That might be interesting for @philm