https://codereview.qt-project.org/c/qt/qtquickcontrols2/+/321362 introduces a way for the new native desktop styles to style the increase/decrease buttons, which aren't necessary for touch. As we're late in the release process, we are trying to make this API private for 6.0.

In 6.1, we should expose a similar API to SpinBox's up/down grouped properties:

https://doc.qt.io/qt-5/qml-qtquick-controls2-spinbox.html#down-prop

The touch styles can then just ignore the properties as they currently do.