I use Nextcloud notes because I already had a Nextcloud running when I needed a notes app.

Oh. I recommend it because I running on your own server your data only in your hands. And it's Foss.

I use Joplin because its lightweight and straight forward to use. Plus it being available on both android and desktop is a bonus.

NoNonsense Notes (A simple notepad and to-do app with an excellent navigation)

https://f-droid.org/packages/com.nononsenseapps.notepad/

Looks interesting....

I just use Zettlr because it was the first thing I saw in the store.

I personally use a messaging app with a chat with myself. I delete "notes" I no longer need.

simple notes pro (I recommend all of the dev apps, they're FOSS https://www.simplemobiletools.com/). It's lightweight, no-frills and has a great widget showing a note content.

I like Obsidian, here's a post showcasing what it is capable of https://mathisgauthey.github.io/my-complete-obsidian-workflow-to-manage-my-life/ - sadly its not open source; have it in Flatseal to restrict files & system access and use portmaster to restrict net traffic of plugins. Logseq is also very good and is open source, but would still restrict in the same way. Zettlr is the best simple & functional open source note taker. If you're an Emacs lover then org-roam works but requires a lot of tinkering (as with everything else in Emacs!). On mobile Zettel notes will read these same markdown notes and you can sync them with a git repo, or use Nextcloud (eg self hosted on Ubuntu with Cloudron).

https://www.f-droid.org/en/packages/net.gsantner.markor/

Simple & supports markdown.