To export only the audio track it is not enough to select "Audio" in the deliverpage and activate "Export Audio". No, additionally the "Export Video" selection must be deactivated in "Video".
In this case It would be logical, to export only an audio clip independent of the settings of "Video".
But why do I need a preset when regular controls (video, audio) are actually self-explanatory. For me It makes no sense to activate audio and get video as export.
But I'm sure we don't need to pursue this further, because there are enough more important topics. Thanks again for the hint