At the moment notes and todolists are stored as Strings in a Database. But notes are just simple HTML. So it won’t be difficult to export them as files into nextcloud - That’s something I had in mind from the beginning
Encrypting files (notes) is already possible. Therefore you need to set a password. This password is stored per hash inside the Database (the server just knows the hash, not the password. Therefore the client application is generating the hash and sends it to the server). This makes it possible to share encrypted files. All users that have access to the encrypted note need to know the password.