As far as I know, version available here on GoG (which is currently 1.2G) might only have local (split-screen) multiplayer. I haven't tested it though as I don't have controller which is needed.
We know that. I've tested it already, using Controller and Mouse enables splitscreen multiplayer.
Doesn't help though, because 1), it's local only, and 2), it seems to be extremely picky about which Controller can be used, as all of my controllers won't keep holding onto anything. It's like trying to grab things with slippery hands, it lets go as soon as you move or doesn't register directional inputs at all every now and then... it's the same issue with controllers in singleplayer.
That's why we're asking for the (online) Multiplayer update.
It's been out for about 1 month or so already!