Project storage: Items from components view that have QmlSource specified for them cannot be dragged into the scene

For example, try to drag "GridView" into the navigator -> the cursor looks like drag is allowed but once you drop it, nothing gets added to the scene.

QtQuick3D has also many types that behave like this (e.g. "View3D"). The common denominator for all these types is that they specify QmlSource in .metadata file.