Mozilla's current catalog of Android apps consists of browsers, but there's something new today. Mozilla has a note-taking app called Notes by Firefox. It's encrypted and syncs automatically with Firefox on your desktop. Don't expect a lot of fancy features, though.
That intro really covers almost everything you need to know about this app. It doesn't have a ton of features like Keep or Evernote, but it's super-fast. It only supports plain text—no formatting, images, or doodles. Syncing happens immediately, and all data is encrypted to prevent spying.
After logging in with a Firefox account, any text you add will immediately zip over the internet to appear in Firefox desktop. You will need the free Notes browser extension, though. This app is "unreleased," so there could be stability issues. There's not a lot here to be broken, though.