This applies to all switchers except Cover Switch and Flip Switch.

SUMMARY

If "Show selected window" is enabled in the switcher KCM, selecting a window in the switcher will raise that window. If the user now (left-)clicks that window, the whole operation is cancelled, and the window that the user started with is raised and focused. 

This is not intuitive, as left-clicking something should select that thing; if a mouse click based way to cancel an operation is required, this should be bound to the right click.

(The same holds if the user clicks an unrelated window that is still visible; that window should be raised and focused, and the switcher should close. This can only happen if "Show selected window" is disabled, I think)

(The reproduction step below activate switchers using Alt-Tab for simplicity in replication, but this is particularly annoying with mouse-only operation by binding the task switcher to a screen edge.)

STEPS TO REPRODUCE
1. Select a switcher that is not Cover or Flip Switch in the Task Switcher KCM; enable "Show selected window" if it is not already enabled.
2. Open several windows, press alt-tab, keep holding tab.
3. Left-click one of the visible windows (that is not the window that the user originally pressed alt-tab on) 

OBSERVED RESULT

The window that the user originally pressed alt-tab on is raised and focused, the switcher closes.

EXPECTED RESULT

The window that the user left-clicked is raised and focused, the switcher closes.

SOFTWARE/OS VERSIONS

Current Neon with Plasma 6.2 Dev; but from my light testing, Plasma 2.27.11 in Kubuntu 24.04 has the same behavior. 

KDE Plasma Version:  6.1.80
KDE Frameworks Version: 6.4.0
Qt Version: 6.7.0


Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION