When I do a fresh start of QtCreator, and create a project that makes use of QtObject or Component.xyz they are marked as either "Invalid property name (M16)" or "Unknown component (M300)":

Even when directly importing QtQml which [is claimed to provide QtObject|https://doc.qt.io/qt-6/qml-qtqml-qtobject.html], the message is visible.

If you add "QtQuick.Controls", the error goes away. Sadly this doesn't help, as qmlsc marks QtQuick.Controls as "unused import".

Interrestingly, sometimes the message disappears for whatever reason, and QtCreator is happy with it.