Didn’t know they actually published some source code. I looked at their GitHub account, unfortunately almost all of their repositories have this in their readme:

This is proprietary software owned by Anego Studios. All rights reserved.

You may NOT sell this software in any way, shape or form. You may NOT distribute this software in its unmodified form.

Which part of it is open source?

And you don’t need the official Steam client to download games. There’s tek-steamclient and steamctl, for example.

I don’t get what that has to do with DRM. For example, I need to have a package manager installed to install packages. Doesn’t mean the package manager is DRM.

How is that any more DRM than GOG requiring you to use their website to download games from them?

How? Steam games don’t necessarily have DRM, they can be the exact same files you download elsewhere. And the Steam client may be proprietary, but no mechanism prevents you from copying it around or using it, other than requiring login data, which stores like GOG also require?