I've found this solution: - builded kguiaddons-5.62 on my pc
- copied src/debian/kguiaddons-5.62.0/obj-x86_64-linux-gnu/bin/kmodifierkey_xcb.so to /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kguiaddons/kmodifierkey/kmodifierkey_xcb.so
Now sddm capslock alert works, keyboardindicator works and systemsettings numlock on/off on start works too·
kmodifierkey_xcb.so is a new file and pkg seems not install it. Best, Luca.