Created attachment 145675 [details]
screenshot showing the invisible window created by Kickoff in effects-overview

SUMMARY
The Kickoff application launcher (and its alternatives) may be triggered while the Overview effect is active using their hotkey and will show up as an invisible window in the Present Windows effect that is part of the Overview.

STEPS TO REPRODUCE
1. enable Overview effect
2. trigger Overview via hotkey (default: Super+W)
3. press the Kickoff hotkey (default: Super) while in Overview

OBSERVED RESULT
An invisible window (i.e. no thumbnail/preview, only icon) called "Plasma" is added to the Present Windows effect in Overview. It interprets the Kickoff launcher triggered by the Super key as a dedicated window and presents it.

EXPECTED RESULT
Either the Kickoff launcher is prevented from being triggered while Overview is active or the Overview's Present Windows effect ignores any Plasma launcher window (or even both).

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE neon Unstable Edition
KDE Plasma Version: 5.24.80
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
Also affects the two Kickoff alternatives (Application Menu, Application Dashboard) that can be selected.