To use the steroids analogy, if you're looking for a sober (minimalist) notes app, checkout Dynalist.io I have most of my life there (lists, plans, journaling, etc) I am not affiliated with Dynalist, just a very happy user
What you want for your notes is:
0) You need to decide what kind of functionality you need in a note management app which cannot be fullfilled with other alternatives such as a simple text editor (I use Sublime mainly for note taking, plus Google Keep for groceries).
1) An open data format so you are not locked in a platform. This allows you far less time if you want to swap service which decreases monopolistic behavior (vendor lock-in) and increases competition (yay capitalism).
2) You deciding the storage location (this then allows you to use Dropbox or Syncthing or Rsync or whatever cloud, but also allows you to use public-key cryptography such as e.g. Cryptomator). It also allows you to opt-out of the/a cloud.
The logical solution is to use an open source application. Though I'm not sure I'd want it to be a browser (saw NPM in the source tree). I'd say the logical place for this kind of data is near your agenda, like Nextcloud.
Any other recommendations for fully open source Notes solutions?
0. This is subjective, but Dyanlist meets this for me. 1. You can export your data from Dynalist as txt or opml 2. While your data isn't exclusively stored there, you can set a backup of your Dynalist data to Google Drive or Dropbox. This works for me.