There is only a small selection pre-set. But you can create your starting position yourself:
You click on "Show Advanced Options", go there to "Game type" and chose "Custom FEN", then a new box opens where you can paste in the FEN of your starting position ...
I would like to create a thematic tournament (daily). When you want to create you get a list of opening names, but they are not always distinct. Is there an overview of the possible starting positions?