Wow, it looks like after removing the JSON export they also removed the bulk export at all. I will mention it in the documentation. Unfortunately there is nothing I can do about it. You might ask the support of NimbusNote/FuseBase if it will be possible in future to bulk export or why they removed it.
I found this tool in a quick search, but it looks non-trivial (the developer reverse-engineered the internal API). Maybe someone else did migrate recently and can share some hints.