SUMMARY
I am using 3 keyboard layouts (English, Ukrainian, Russian) and most of the time I am using two keyboard layouts (English and Ukrainian or English and Russian). To quickly change the keyboard layout I use the "Spare Layout" option (All Settings -> Input Devices -> Keyboard -> Layouts -> Spare Layouts). If I need to change a pair of keyboard layouts I using mouse and tray. Over the past few months, the keyboard layout with the mouse has not changed at all. The menu opens and responds to keys, but does not change the keyboard layout.

STEPS TO REPRODUCE
1. Add more than two keyboard layouts
2. Turn on "Spare Layouts" and set "Main Layout count" to 2
3. Check "Spare Layouts" (Switching must be between two keyboard layouts)
4. Click right button of the mouse on the tray with languages
5. Select the spare language with the mouse and press the left button of the mouse
6. Check tray icon, must be with symbol/flag of new language
7. Now one of the languages will be replaced by a new one and again you can switch between the two keyboard layouts

OBSERVED RESULT
Language is not changing and icon too with the mouse

EXPECTED RESULT
Renewal of the ability to change the keyboard layout with the mouse and with the ability to change the backup layout


SOFTWARE/OS VERSIONS
Fedora release 34 (Thirty Four)
KDE Plasma Version: 5.85.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
kwin-libs-5.22.5-1.fc34.x86_64
kwin-common-5.22.5-1.fc34.x86_64
kwin-x11-5.22.5-1.fc34.x86_64
kwin-wayland-5.22.5-1.fc34.x86_64
kwin-5.22.5-1.fc34.x86_64