https://doc.qt.io/qt-6.5/qobject.html#Q_OBJECT

The main paragraph emphasizes that the access modifier should be private. This is an old requirement. Starting with 6.5, adding Q_OBJECT adds the private access modifier by itself. Users no longer need to add the macro to a private: section. So, the main paragraph is not completely valid anymore.

The same is valid for Q_GADGET and other similar macros.

The Meta-Object System topic also mentions obsolete requirements.