KopiaUI is not an app that you can start and stop, it’s a background service accessible through the system tray. Running on a Gnome desktop, with no system tray, the first time you start kopia-ui it opens with on the repository page. If you stop and start kopia-ui, it will only start the system tray icon.
I was hoping to use this as a self-service archive for a 2PB home directory with ~500 users. Their virtual desktop is Gnome on a shared server, 36 user sessions per node. I don’t need 36 kopia server processes sitting in memory, especially being infrequently used by 10% of the users.
Hopefully this helps someone out. I spent 2 days working on it before realizing this.