Me again.
First thing:
Harmony does not try any longer to install the font, so manual install of the font did work.

But I just found a thing which looks like a bug to me:
Copy item/Paste-Paste before and
Copy item/Paste-Paste after
do not work as I would expect.

I right-click on a note, lets say a high D (second line from top) with a duration of 1/8, and select "Copy item".
I then right-click on any note and select "Paste-Paste before" (or "Paste-Paste after").
Instead of the expected 1/8 high D I get a 1/4 G (second line from bottom)
It seems as if always a 1/4 G is inserted instead of the note that was copied.

Also, I just activated the toolbars "Notes" and "Pitch" - they do look as if there is something gone wrong...
See picture of toolbars
It is possible to change the positions of the "pressed" areas of the toolbars, but there seems to be no reaction...