In QtC, quickfixes from the language clients should be appliable using the quickfix shortcut (Option+Enter on macos, for example).

While this works for C++ code like:

This does not work for QML code like:

You can apply the quickfix in QML code by clicking the lightbulb, but not via the shortcut.

Qmlls is set up as following:

I attached the example project, where the screenshots were taken from, as untitled20.zip.