Hey, thanks for the feedback. So I am not sure if you grabbed the latest update, but this past release has some features with codex that may be close to what you are asking for. To get it, just download the app and install it again.
Be sure to take a backup in settings before this version, just cause it was a lot of changes. The new features allow you to nest notes in both campaign codex and session planner. Here is an example; just let me know if you mean something else. Your data should be safe so you shouldn't need to restore the backup, but it's best to take one in case