Duplicati generally has a lot of pieces that go together in many ways, and this can cause problems/confusion.
Seeing the tray icon is fine, and it takes your browser to Duplicati, however the web server is Duplicati server.
Generally the server is accessed at http://localhost:8200, but if 8200 is in use, the NEXT one takes 8300, etc.
One generally doesn’t run multiple servers, so you may wish to decide if you prefer the service which runs at boot and can backup any user, or if you want Duplicati to run at login, and lacks VSS for non-Administrators.
Out-of-the-box, the current install does the latter nicely, and if the user is an Administrator they can get VSS.
Service is more trouble now, and requires editing Windows shortcuts, e.g. on the desktop and login autorun. Sysinternals Autoruns or Google can help find it, and you can edit the desktop shortcut directly by right-click. One problem is the next Duplicati install from .msi will write over your custom shortcut, but you can rename it.
If you don’t need a tray icon, you can omit the previous paragraph and use a browser shortcut or something, however you also have to deselect some things during the .msi install, or it will helpfully create the shortcuts.
For your VSS, if user is an Administrator and you just need backups when logged in, you don’t need service other than the one that’s built into the tray icon, but if you fall the other way, you probably want to push tray icon’s version of the service aside by adding --no-hosted-server to its shortcut (probably in the Target field).
Still not a complete step-by-step, but I hope that helps clear up what’s going on. Thanks for wanting to learn.