Have you tried the profile note feature on Mastodon?
✅ You can add your own notes to people's profiles on Mastodon: go to their profile page and click on "click to add note". Only you can see the note.
It's useful if you want to keep track of people you're interacting with, especially if their profile biogs are incomplete or absent. (For example if someone developed a particular app but their profile doesn't mention it, you can add a reminder for yourself.)
@feditips
thanks, I wondered what that feature was meaning, really a bit mysterious until I saw your explanation
@monumentale
Yup, that's it exactly, it's a little note about the other person, but only you can see the note.