I’m running the Gnome Desktop on Ubuntu 18.04. I installed Duplicati - 2.0.4.23_beta_2019-07-14 and the mono prereqs. It seems to be working ok, with control from the web GUI.
But I keep seeing references to a Tray in the documentation.
There is no evidence of one on my desktop.
Also the install doesn’t seem to have integrated systemd. I’ve been just starting the duplicatii-server manually. Don’t know if thats related.
My install created a /lib/systemd/system/duplicati.service which is presumably what I see with systemctl list-unit-files | grep duplicati. I can systemctrl start duplicati.service, however to your tray icon point, the tray icon is in Duplicati.GUI.TrayIcon.exe, and has a built-in Server.
Other Command Line Utilities talks about some of the differences. If you prefer the TrayIcon, and don’t have any particular need to start Duplicati at system start, or to access files your user has no access to, then one way to do that is to run the duplicati command yourself after login. It’s possible (at least on Windows) to run Duplicati.Server.exe at boot, and also manually launch a TrayIcon to see server status, however you need to use the --no-hosted-server option otherwise it will also start its own internal server.