So these two packages are the alternatives for supplying the desktop trayicon.
If they are not present the duplicati binary cannot run because it cannot show the tray-icon on the desktop.
You can still run the “headless” version, which is duplicati-server (aka mono Duplicati.Server.exe) that does almost the same as the tray-icon and starts a web-server.
If you are just looking for the commandline interface, duplicati-cli (aka mono Duplicati.CommandLine.exe) it also works without the mentioned libraries.
Both of these work with just the mono runtime installed. You can see the exact packages here:
Installing these packages (ignoring the libappindicator ones) you can run from the zip file.
As mentioned by @ts678 we are working on a new build that does not rely on this, and the new builds also have non-GUI packages to allow slimmer installs with fewer dependencies.