I know this is possible as I have seen others set this up in person but I am not able to get the correct behavior: editing on my local files and automatically updating in copy files on remote host.
I have configured a remote host in Intellij to connect to a linux based server(local is windows) using the SFTP with a SSH configuration. I have mapped a local directory to a remote directory. When right clicking on my local directory in my open project under deployment I can sync to my mapped directory. Yet, any changes I make are not automatically updated on the synced files.
You need to set Settings | Build, Execution, Deployment | Deployment | Options | Upload changed files automatically to the default server to Always or to On explicit save action:
Also make sure the server is marked as the default deployment target: