After installing a host of kf5 updates today I find that several applications complain when an action is invoked. As an example: invoking Evolution from a tray icon produces the error message “Unable to create io-slave. klauncher said: Error loading ‘/usr/lib64/qt5/plugins/kf5/kio/file.so’.” This message occurs with other actions as well.
Then it’s probably one of those updates where a reboot is necessary for changes to take effect (an example of an update transaction that supports the behaviour of tools like gnome-software that now update on reboot).
You can install the tracer dnf plugin, which tells you what processes need to be restarted after a dnf transaction: