The property currentValue is conflicting making the qml file not run.
Thanks for noticing! The currentValue property was introduced with QtQuick.Controls 2.14 (Qt 5.14). Very convenient, unfortunately Plasma 5.18 must support Qt 5.12.
BTW. QML import system is stupid (or I am :) ). Apparently, using import QtQuick.Controls 2.5 will not allow you to use currentValue, but it will still conflict...
Instead of removing currentValue change it's name. This property is used in KeySequenceItem
I won't work in Qt =< 5.13. Just rename currentValue to something not-conflicting.