You may self-host your notes or calendar, but you’re forced to either recreate account systems or give up on interoperability.

I literally just finished setting up Radicale on my old laptop, and now I can access my calendar and contacts through CalDav and CardDav from every single client under the sun. Maybe don't use AI to write your entire article. I won't even bother reading the rest of the article if you don't even get this right.