From https://doc.qt.io/qt-6/qtmodules.html and then going into the Qt Quick Controls page https://doc.qt.io/qt-6/qtquickcontrols-index.html then clicking into the "C++ Classes" URL, the page doesn't exist.

https://doc.qt.io/qt-6/qtquickcontrols2-module.html (trying without the '2' also shows a 404).

The page does exists in the latest snapshot from dev https://doc-snapshots.qt.io/qt6-dev/qtquickcontrols2-module.html