GOG and Steam versions can play together using Direct Connection or LAN. I'm not sure if lobby compatibility is being looked at.
i'll look for a bug reporting feature and upload a ticket then, because it's quite an important thing
game list for multiplayer shoulkd have all active open games being played atm, right? if steam and gog games can connect to each other but they cant see each other then the feature of game list is not working as expected
it's kinda logical