I don't even think that this new client supports anything but GitHub. Their previous Windows client didn't.
Yes, it did, but it had very basic functionality. The new client still supports non-GitHub repositories (tried with private GitLab repos).
I wish it had the code review, commenting, issue tracking of the web app in a desktop application, all in one place. It's a pain to move constantly between the editor, CLI/SourceTree and Github web app for everyday tasks.