SUMMARY
First of all, I'm not sure this is a bug in yakuae, kwin, the window switcher or what component.

Since the upgrade to frameworks 5.85 and gear 21.08, yakuake doesn't show up in the window switcher (Alt+Tab) anymore and loses focus if you open for example something from the system tray.


STEPS TO REPRODUCE
1. Open a couple of apps and open yakuake
2. Press Alt+Tab (yakuake doesn't show) and go to another window
3. Press Alt+Tab again, you won't end up in yakuake but in another window

OBSERVED RESULT
yakuake doesn't show up in the window switcher and loses focus

EXPECTED RESULT
yakuake does show up in the window switcher and keeps focus

SOFTWARE/OS VERSIONS
Operating System: Slackware 15.0
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.85.0
Qt Version: 5.15.2
Kernel Version: 5.13.11 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i5-1035G1 CPU @ 1.00GHz
Memory: 15.2 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics

ADDITIONAL INFORMATION