SUMMARY
"Spare layouts" setting does not work. 
I do see that `systemsettings5` updates `~/.config/kxkbrc` file:

[$Version]
update_info=kxkb_variants.upd:split-variants,kxkb.upd:remove-empty-lists,kxkb.upd:add-back-resetoptions

[Layout]
DisplayNames=,,
LayoutList=us,ru,ua
LayoutLoopCount=2
Options=grp:lalt_lshift_toggle
ResetOldOptions=true
ShowFlag=false
ShowLabel=true
ShowLayoutIndicator=true
ShowSingle=false
SwitchMode=Window
Use=true
VariantList=,,

But nothing happens after, I still see all three languages in my loop.

STEPS TO REPRODUCE
1. Open system settings
2. Add 3+ (us,ru,ua) layouts to your keyboard settings
3. Select "Spare layouts", and ensure that your "main layout count" set to 2.
4. At this step you should have two (us,ru) main layouts, and one (ua) additional.

OBSERVED RESULT
All three languages could be switched using the main shortcut.


EXPECTED RESULT
Only the first two (us,ru) must be available through the main shortcut.


SOFTWARE/OS VERSIONS
Fedora 39, KDE/Wayland
KDE 5.27.8
KDE frameworks 5.110.0
Qt 5.15.10
Linux 6.5.6
AMD Ryzen 5 PRO 5650U with Radeon Graphics

ADDITIONAL INFORMATION