This thread is for questions, feedback, and bug reports related to co-op specifically. As noted in-game, co-op is VERY experimental, and your feedback will help improve it!

Quick FAQ

How do I start co-op?

After you’ve started a game, open the pause menu (press Esc), click the co-op button. Don’t forget to choose a controller or keyboard for the second player in the input options! (This can take a few attempts before things work…)

How do I play over the network?

There are reports you can add non-Steam games to your Steam library and play via Steam Remote Play as long as you’ve enabled Remote Play in your Steam settings. This is untested, so if you find success doing this, let me know!

Otherwise, there are programs like parsec.app and Moonlight / Sunshine you could try.