At the moment when you open file on mobile you can't save it back. You need to use "Save as" feature, store it somewhere and then manually reupload.

This is to allow saving file back directly to S3Drive.

The workflow could be as follows. When user open a file, we then save download a file to temporary location, set up the file watcher and open using external app.

If external app does modify the file, we would pick up the change (based on last modified) and sync automatically.

Related: https://s3drive.canny.io/feature-requests/p/android-mount-point-save-to-share-support