I still think a syncthing client of some form is ideal. As someone else mentioned there is the option of using the Syncthing Tray devs experimental android build. To avoid issues with sync-conflicts / maintain high-availability access to the most recent file, I sync the databse to a raspberry pi with the encryption option selected (not that the pi is untrusted per se, but it is a device that doesn't need access to the file, it just serves the most recent changes to other devices since often my laptop / phone / desktop are not all on at the same time).