Thanks for your comments - but I still seem to miss something...
When opening '.../JUCE/examples/audio plugin host/Plugin Host.jucer' on my Mac in the projucer I get the following error:
'base/source/baseiids.cpp' file not found
When pushing on the [Save and Open in IDE] button, however, no error is shown and, after compilation, the 'Plugin Host' starts up without any problem.
Opening the preference page via "Projucer > Preferences..." the following path is shown for VST3 SDK:
The file baseiids.cpp is here:
In the "Exporter Settings" for Xcode the attribute "VST3 SDK Folder" has the value:
Any idea what is going wrong?
Thanks for you help,