On MacOS Monterey 12.0.1 (but also on some other machines), it works exactly once. After that, double-clicking the icon doesn’t do anything any more and I have to manually type localhost:8200 to access the web interface.
I’m not a Mac user, but does Duplicati appear in the status bar along the top right part of your screen (after you run the icon the first time)? That’s basically how it works on Windows, and you can bring up the web UI by clicking that icon.
Not that IO have seen.
The first time, the app does something and the browser opens on the duplicati page.
After that, no effect.
However typing localhost:3200 does connect to the page and it works - so the underlying process is active.
Luca