A year or so ago the "unique" setting for virtual KDE desktops was removed, reducing functionality & flexibility of KDE. This still does not seem to have been rational, necessary, or helpful. In fact the issue of users wanting unique virtual desktops has been a reoccurring forum issue, e.g. viewtopic.php?f=83&t=127712 , viewtopic.php?f=285&t=127632 , viewtopic.php?f=15&t=139142 , viewtopic.php?f=289&t=160351

A cynical person might almost suspect that a section of the developer community decided to remove the function in order to force users to use a slower resource hungry "Activities" function instead of using the existing fast virtual desktops setup for various activities. I certainly hope that wasn't the case, and it would have been a unnecessary punitive action if it had been. I'm sure if KDE was allowed to have unique virtual desktops again that "Activities" would still have a proper place. There is a place & utility for the "Activities" function, **BUT NOT** as a replacement for unique virtual desktops that use to make KDE a powerful environment (currently Xfce seems to be the only option for those of us who use to use KDE's unique desktops).

Instead of taking the 'unique' desktop function away from users, I suggest the "Activities" function is better aimed at allowing your workstation to service different parts of your life for example for work & home use, or when you do volunteer work while using your own workstation; you can use "Activities" to switch between a set of virtual desktops setup for work to to setup for leisure or other parts of your life, "Activities" can help workstations better service different parts of a user's week while unique virtual desktops provide a powerful environment within each part of your week.