I'm having the same problem. I chose to get the game on Steam, GOG, and Stadia. I just wanted to support the project. I noticed that I can launch the GOG version with no launcher, and access my steam saves just fine. Both PC versions are on separate hard drives.
I know, it's kind of redundant, but interesting in that my Stadia account is the only one not cross saving, and Stadia can not play the game with any of my friends on PC. I would like the convince of playing on my TV console style. It is early release, so I understand not everything is ready, but I wish they were not so silent about it.
