Without editing any, does it still start for you from the PrtScn key?
Asking since a rebuild is obviously needed, checking if it is just the .desktop file that needs adjusting (and subsequently will need an upstream bug report, if that fixes the issue).
Edit:
Forget the above, this file /usr/share/applications/org.kde.spectacle.desktop
runs with just qdbus, will need qdbus-qt5 for KaOS, fix will be up shortly.
So it should read:
Exec=qdbus-qt5 org.kde.Spectacle / StartAgent