Hello,
Are you trying to build and run for Mac or iOS? I see from your notes that when you created the app, you selected Mac (clang 64) and iOS. Do you see this error when you select Mac or iOS or both?
Typically the only thing you should need to do is run the post installer and point it to the desired versions of Qt. Once you do this, you should notice in your Qt kit, that there will now be an ArcGIS folder in the following location (<qt_install_path>/Qt/clang_64/qml/ArcGIS). If this folder does not exist, re-run the post installer. If it does exist, make sure you are selecting the proper kit from Qt Creator.
Thanks,
Luke