When I update to the latest version of Plasma 5.21.0, it can't work.
Here is the detail:
file:///usr/share/plasma/plasmoids/org.kde.windowbuttons/contents/ui/main.qml:26:1: plugin cannot be loaded for module "org.kde.appletdecoration": Cannot load library /usr/lib/qt/qml/org/kde/appletdecoration/libappletdecorationplugin.so: (libkdecorations2private.so.7: cannot open shared object file: No such file or directory)
When I update to the latest version of Plasma 5.21.0, it can't work.
Here is the detail: