If you've been around KDE for a long time you remember that you could have different wallpaper for each different virtual desktop.
This feature disappeared somewhere in between KDE4 and KDE5, was said to be impossible, then promised by one developer, only to get side tracked.
Its been two years. TWO YEARS, and 200 posts on the bug report:
Finally one clever guy, Jonathan Marten, found a way to do it with a tiny utility that hijacks the slide-show wall paper option to change wallpapers as you switch desktops.
Scroll down the page, there are step by step instructions (6 easy commands) in a clear writeup. and it works. Flawlessly.
Wow have I missed this feature. Boy Am I glad to have it back.