SUMMARY
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***

Previously, in KDE 5, when I pressed Alt+Tab+Tab very quickly (and released it), then I have the second window in front of me, effectively immediately.

Now, in KDE 6, after the same sequence, I have a ~700 ms delay before the window is shown and after that the tab box visualisation is even flashed for some ms (basically, just its borders are drawn, its content I can't see because it disappears very quickly).

Simple Alt+Tab is also very slow and suffers from the same.

If I turn off the tab box visualisation in system settings, this delay is gone.

This is the default tab switcher which comes with KDE 6 (first item in the list; I have it in another language).

EXPECTED RESULT

Either the tab switcher is displayed immediately and introduces no delay or not displayed at all and, again, introducing no delay.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20240318
KDE Plasma Version: 6.0.2
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.9-1-default (64-bit)
Graphics Platform: X11
Graphics Processor: NVIDIA GeForce RTX
System Version: 1.0

ADDITIONAL INFORMATION