Just for a quick clarification - it actually refers to manual file sync on your need at the moment. Syncing files automatically is something the team is discussing right now but may not become available in the product in the near future.

Under the hood, essentially, you can access Nimbus workspace via ssh (with private key/public key pair). With that foundation, if you ever want to download files or upload files, you can do so with scp, rsync, or anything that can transfer files over ssh tunnel.

That also means, technically, you don't have to use VSCode/JetBrain to write code on Nimbus workspace (though we have/are going to have official extension/plugin support, which is recommended). You can directly ssh into the workspace and write code in emacs/vim, or use any editor/IDE with SFTP support.