Assume I drag one *.mp3 onto Audacity then a wavform is shown. Fine.
Now I drag a second *.mp3 onto Audacity then the existing Waveform is shrinked by 50% so that a second Waveform fits into the window too.
How can I tell Audacity to automatically close an existing Waveform when another, new *.mp3 is dragged onto Audacity?
Only ONE Waveform should be displayed at a time.
Presumably this is because you turned on “Automatically fit tracks vertically zoomed” in the Tracks Preferences, which you asked about here https://forum.audacityteam.org/t/how-to-auto-maximize-audiotrack-sub-window-when-loading/23581/1 .
You cannot. But you can use File > Open instead of dragging the file in, or right-click the file in Explorer > Open with, either of which opens that file in a new, empty project window.