Welcome to the forum @walrusbarretterura
Instructions are kind of scattered, and I guess Windows got Configuring the Duplicati Tray Icon in Windows but Linux didn’t get specifics. The general plan is similar though. Here are some other places that describe.
The TrayIcon package
Duplicati.GUI.TrayIcon.exe
Installing Duplicati on Linux (Ubuntu / LinuxLite)
Note that on Linux, you get to Duplicati.GUI.TrayIcon.exe through the /usr/bin/duplicati script. I’m not certain how to launch at login, which is actually the usual Windows way, where a service is hard to setup whereas on Linux the service is the default and the TrayIcon (which includes the server, unless told not to) is harder.