Id love an app like notion. i currently use nextcloud for personal notes, calender, and other things. I know highlighter is in it's infancy and seems super promising.
Beyond notes I use my RSS feed a lot.
Discussion
An easy-to-use note-taking app with encryption, advanced realtime collaboration and syncing functionalities seems like a very reasonable idea. The collaboration feature can even create a network effect.
I was even planning to build something like this for myself. I should definitely look into it.