Hello!
Do you hate the watermark preview banner?
Add the text HideDesktopPreviewBanner=true just after [General] in the file ~/.config/kdeglobals. You will have something as the following:
[General]
HideDesktopPreviewBanner=true
Better for OLEDs displays, stylish, auto-suspend all-blacks displays, etc.
Buddy, this message was posted 6 month ago, when this issue was a thing. Does not applied nowdays. But thank you for your help.
Saw it too late, this community is pretty dead.