The short answer to this is no: the file system repository is read-only by design from inside Moodle as far as users are concerned. You would need to use another repository type to allow users to upload or save files into the repository from inside Moodle.
Having said that, you are not limited to using just (S)FTP to upload files to the repository: you can use any method your server will support to put files there, as long as you are willing to set up the correct permissions and provide some alternate interface for users outside Moodle.
If WebDAV will not work for you, you might consider looking at the NextCloud integration, which is at least based on open source OwnCloud and can be installed locally.
Having said that, you are not limited to using just (S)FTP to upload files to the repository: you can use any method your server will support to put files there, as long as you are willing to set up the correct permissions and provide some alternate interface for users outside Moodle.
If WebDAV will not work for you, you might consider looking at the NextCloud integration, which is at least based on open source OwnCloud and can be installed locally.
