Usually in DE's when you start copy files there window appear at center of screen (progress of copy process). But in Kubuntu 18.04 it only gonna be shown at the notification area at the panel. It's confusing: sometime I think that there some bug and copying process didn't begin. So I repeat it several times, until I notice progress circle on the panel. How could I make it less confusing ?
KDE Frameworks 5 and Plasma 5 notifications
As default the plasma 5 desktop is showing copy progress in the task buttons and in the notifications:
Task manager setting: "Show progress and status information in task buttons"
Notification Settings: "Track file transfer and other jobs"
If both (task button progress & notification transfer) settings are disabled the traditional file transfer window will be shown:
Plasma setting changes may need to restart the plasmashell - logout and login.
KDE Forums: Dolphin not showing native file transfer dialog - https://forum.kde.org/viewtopic.php?f=224&t=135264
In later versions of Plasma (e.g. 5.23) those settings are grouped under "Notifications"