SUMMARY
Tasks can be dragged onto the activity switcher in order to move them to the new activity. 
Looks like this: https://imgur.com/7eN37wb
Unfortunately this awesome feature stops working, as soon as there is more than one Window open of the same application. If a task with multiple Windows is dragged onto the activity switcher, the options "Move to this activity" and "Show also in this activity" are displayed, but the drag and drop does absolutely nothing.
I tried to hover over the application icon in the task bar to show the individual task windows, and then drag an individual window onto the activity switcher, but this does not do anything.
I illustrated the problem here: https://imgur.com/a/C77SOCF


STEPS TO REPRODUCE
1. Open two Windows of the same Application (e.g. 2 Dolphin Windows)
2. Open the Activity Switcher
3. Drag the Task onto the Activity Switcher

OBSERVED RESULT
Nothing happens

EXPECTED RESULT
The task is correctly moved to the new activity.
The optimal behavior would be to be able to drag either the application icon directly, resulting in all windows of this application being moved, or dragging individual windows from the hover-popup onto the activity switcher in order to move only the respective window to the new activity.

SOFTWARE/OS VERSIONS
Operating System: Kubuntu 21.10
KDE Plasma Version: 5.24.1
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.2
Kernel Version: 5.13.0-28-generic (64-bit)
Graphics Platform: X11
Processors: 16 × 11th Gen Intel® Core™ i9-11950H @ 2.60GHz
Memory: 31,0 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics

ADDITIONAL INFORMATION
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