buttons property of the
KQuickAddons::ConfigModule class does not visually change the buttons in the systemsettings application, can this be considered a bug? (in details 477718 – Buttons do not update when ConfigModule.buttons property is changed,)
It seems like the way is to use
ConfigModule.buttons, see kcms/touchscreen/ui/main.qml · master · Plasma / Plasma Desktop · GitLab.
Also another way is to not access it via QML, and do it on the C++ plugin side. See kcms/gamecontroller/kcm.cpp · master · Plasma / Plasma Desktop · GitLab.
Do the examples you provided mean that this property can only be used during initialization, and cannot be changed later?