SUMMARY
***
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***
If you want to sort manually the apps in the favorites part of kickoff after you select the item and drag it to the desired place the app does not deselect itsfel as it does, for example, in the icons only task manager bar. If you want to move another app after the initial one it will not happen but the first app will move again. If you try to click on an empty space in the favorites portion of kickoff then the (first) app will open/start.

STEPS TO REPRODUCE
1. click and drag app in favorites
2. release finger of the left mouse click
3. click on another app in favorites and still the first app will move 

OBSERVED RESULT
the initial moved app is not deselected

EXPECTED RESULT
 the app remains selected

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: opensuse tumbleweed/kde plasma 5.27.7
(available in About System)
KDE Plasma Version: 5.27.7
KDE Frameworks Version: 5.108.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
this happend on archlinux too, and then the version of kde plasma was older (5.27.6)