While trguing is running: double-clicking a .torrent icon, or dropping it on the window, causes the app to react to it (i.e., you get the "add torrent" dialog box, preset to the currently-viewed server.)
It seems that if trguing is NOT running, when you double-click a .torrent icon (e.g., on your Desktop or in your Downloads folder), the app will launch but the file itself is ignored. You can go back and double-click the .torrent icon and then it will be added.
Tested on v1.5.0 with macOS Sequoia 15.7. Can anyone confirm?