So, in order to connect your Steam library to your GOG one, you’ll need to sign into an active Steam account via the GOG Connect page.
GOG Connect, you see, is a new initiative from the CD Projekt Red-owned distribution platform that allows users to add some DRM-free Steam games to their GOG libraries.
“You own the games, so why buy them more than once?” asks GOG Connect’s tagline, which totally seems fair enough.
Playing GOG versions of games with Steam friends “depends entirely on the game”, adds the Q&A, and for now cloud saves, achievement and friends lists are non-transferable.