Yes, at the moment only Linux is supported for the server. But please upvote the relevant issues so we know which other platforms people are most interested in running Code server on: https://github.com/Microsoft/vscode-remote-release/issues/24
Thanks for the info - I think I would personally be much more interested in trying out VSCode as my main editor if I knew I could also SSH Remote to MacOS as well as Docker containers and the like.