I've tried multiple ways to create a new branch (sub item) in Favorites list: drag and drop, clicking, from various menus, etc., but nothing works. I only get a New Branch as an item directly under Favorites, which does me no good. Hope you can help me. Dopus is a great program, and I have been using it for years. Still learning what it can do!
If you're editing the list in Preferences, click the New Branch icon above the list:
If you're adding a favorite outside of Preferences, click the New Branch button at the bottom of the dialog:
(If you're using Opus 11, I think it was the same in that, from memory, but I can check if you don't see the same options there.)