Two years ago I had an iPhone and, back then, the native "Notes" app worked pretty well for me. However, when I changed to Android I had some trouble finding a similar app or a different one that would fit my needs. For some time I used Google Keep, but I didn't like how the main view would show you the whole note (instead of having only one line per note, which allows more notes to fit in the screen). I changed to Evernote for some time—which was definitely more suited for me—but there were too many ads about getting premium features and, since I didn't need them, I eventually got tired of it.
Back then I already knew what Markdown was, since I had used it to build a website, and I realized that an app with Markdown support could be a very good alternative. I looked around and finally found Joplin, a free/libre and open source app that supported Markdown as well as synchronization—perfect for my needs, since I like having notes backed up in case I lose access to my phone. I have been using it for half a year and so far it has been a great app. I type my notes with Markdown and once I'm done it renders them beautifully. It also lets me backup a copy with Nextcloud which is good since it doesn't force me to do it through Google Drive/Dropbox and on top of that I can set up end-to-end encryption for my backed-up notes! I haven't paid a lot of attention to what algorithm is used to encrypt since I trust my Nextcloud provider, however, I know metadata is not encrypted (I'm guessing to make synchronization faster), but that's fine with me. This also allows me to synchronize my notes with my computer, something that I had never thought would be useful before, but as I use my computer more and more (and my phone less and less), it is becoming very convenient.
Moreover, since I use it on my computer and I can arrange notes with the use of notebooks, it is becoming more of a personal wiki than a note-taking app. I have a notebook named "Notes", but the remaining notebooks hold information in a less "casual" way. I suppose everyone uses notes that way, but being able to use Markdown allows me to store lots of information in a more convenient way, especially when dealing with links and fragments of code.