Hi, Plasma developers!
There was an excellent feature in older versions: a user was able to set individual widgets sets and/or wallpapers for any virtual desktop. I. e., each virtual desktop had its own unique wallpaper an a set of widgets.

Now this feature is not implemented. It's very sad, as this feature was very useful (eg, when switching desktops a user can visually distinct which desktop is active now).

Plasma developers, return this feature in new versions, please.
__________
Am I write in an right place?

Have you tried using Activities instead of Virtual Desktops? Nowadays they operate very similarly, but that Activities provide additional flexibility over Virtual Desktops, including the ability to have separate wallpaper and widgets per Activity.

The only solution appears to be to dump Plasma and use Xfce desktop instead of KDE's, you'll be rewarded with speed , power and configurable virtual desktops.
You can still have any Qt/KDE applications and services you want but have flexibility of virtual desktops again instead of being told that you must use 'Activities' or lump it. Also Evolution provides a good alternative to the Kmail/Kontact suite.

Seems a little short-sighted to abandon the whole desktop just because you don't like how some piece of functionality is presented. Activities are a lot like Virtual Desktops, but provide the additional configuration that you're looking for.
"You do not like them, so you say. Try them! try them! And you may. Try them and you may I say"

(it seems to me that the biggest problem with KDE's Activities at this point is stigma; unless you encounter an actual deficiency)