The overload of QString::arg() in C++ that gives possibility to substitute arguments in one pass is very useful.
See https://doc.qt.io/qt-5/qstring.html#arg-14 for motivation.

Unfortunately this isn't supported in QML.

Simple,

readonly property string text: '%1, %2'.arg('Hello', 'world!')

in Qt 6.3.0 generates error

Error: String.arg(): Invalid arguments 

So the suggestion is to make it available in QML as well.