The Tray Icon
When started, the Duplicati Tray icon tool creates a small icon in the System Tray for easy access to the Duplicati Web Interface. The server component is included in the Tray Icon tool. After a default installation, the Tray Icon tool will be automatically started after a user logs on, making it unnecessary to configure the server component in an everyday use case.
EDIT: This is Windows behavior of the .MSI installer. Duplicati.WindowsService.exe can add the service if discovered and added, but non-Windows might go the other way (Tray Icon is discovered and added).
Configuring the Duplicati Tray Icon in Windows probably matches macOS, but Tray Icon might be called “duplicati” as it is on Linux (and /usr/bin/duplicati-server is a script wrapper to start Duplicati.Server.exe).
Duplicati.GUI.TrayIcon.exe has details including --no-hosted-server for those wanting a separate server. Your case can probably run fine with cutting down the permissions to root, but this isn’t always the case.
Not sure if you’ve noticed, but you found a better spot to post on the password issue, so I pointed here.