Personally, I'm using the next cloud notes app. It's somewhat limited - essentially just plain text with a bit of markdown support, but the upside is that my data is stored in plain text files that are easy to backup and/or export if I ever decide to switch to something else.

I'm running it on an unRAID server with nightly backups, but you could just as easily run it from a raspberry pi.

Before next cloud, I was using text files in Dropbox.

My employer just started using notion. It seems fine so far, but I don't see myself switching away from next cloud any time soon.