Good to know at least something’s working as predicted.
If there was no Duplicati icon at the time when duplicati --no-hosted-server was up and seemingly running (sitting there on top of your shell prompt, not complaining), then it may take some more guessing.
libappindicator is (I think) needed, if you can see whether that’s installed. Maybe someone else has ideas.
$ dpkg -s libappindicator3-1
Package: libappindicator3-1
Status: install ok installed
might be a good thing to check for.