1. In Qt Creator, open the "Examples" tab of the Welcome mode.
2. Search for the "Embedded QWindow" example and open it.
   No source file will be opened. In "General Messages", you can read:

   Project ERROR: Unknown module(s) in QT: macextras
   

   The project can neither be built nor run.

This situation makes no sense to me. If the example is meant for Mac only, it should not be shown on Windows. If it is shown on Windows just to read the code, then a source file should be shown when opening the file. Long story short, at least one of these symptoms should be fixed:

• The Example is listed in Qt Creator Welcome mode.
• When opening the example, no source file is being opened.
• The project can't be built on Windows.

Found by Henri.