Cannot import backup file on iPadOS. A bug?

I created a mindmap and would like to export the backup file of the whole mindmap and share it with my friends. However, it seems that I can’t open .marginpkg files in MarginNote. There isn’t any open in MarginNote option. I’m currently using iPadOS 13.1.3.
Please help!

Thank you very much for the awesome app!

I have the same problem. After a reset I need to restore my notes, but can’t open .marginpkg files.