Wasn't the syncthing android app deprecated relatively recently?

It was if you install it from google's app store, but it's still fully functional for now if you install it from F-droid.

I've been using Obtainium to install Android apps from Github releases and automatically update them. It's worked great.

Syncthing's .apk release files can be found here: https://github.com/Catfriend1/syncthing-android/releases

Syncthing-fork (of the android app, not syncthing itself) is a straight improvement.

Yes, I use this and it is pretty solid. I can recommend it

I can second Syncthing. I just use a simple markdown editor with Syncthing on Windows, Android, and a Linux.