Jellyfin doesn't seems to scan subfolders

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You're using an unsupported folder format.
Each folder in a library is meant for a single movie. You are allowed a single subfolder in depth for things like extras for any particular movie.

Thanks for your answer.
You mean that I cannot have a folder with a collection of movies (like "Star Wars") and then a folder for each one inside?
This seems a serious limitation, because it means that to make it work I need to spread all my Star Wars movies inside the Movie directory (= Library), having them everywhere.