Here’s an example. Main folder is A-Z Notes (that is the folder that you would set for sharing - anything in this folder will be shared including subfolders) - the notes are listed alphabetically. For topics that may have many notes, you can make subfolders such as Finances and Wills. I wouldn’t get too fancy by adding a lot of subfolders (see caveat). Again, do a small trial and see if this works before you commit.
Caveat: I have not had any problems with syncing Apple Notes across my devices but some have. In my current usage I have no more than 10 notes. So, I’m not an Apple Notes power user. See: Update: Needing Serious Advice re: Losing Faith in Apple Notes
You can achieve what you want in Craft, but someone mentioned that Craft does not use end-to-end encryption, so that may be a consideration for you.