Found this post in another thread.
It has the quickest way to get steam working. I just did it myself and can confirm it works on Windows 10.

Use this (correct) links: https://github.com/FriendsOfGalaxy/galaxy-integration-steam/files/11104861/backend_steam_network.zip

https://github.com/FriendsOfGalaxy/galaxy-integration-steam/issues/159#issuecomment-1489195530


Instructions:
- Shutdown any GOG Galaxy client, MAKE SURE.
- Extract the archive contents into "%LOCALAPPDATA%\GOG.com\Galaxy\plugins\installed\steam_ca27391f-2675-49b1-92c0-896d43afa4f8" folder.


Thank you Lobuno for the post which I copy pasted here.


Fix originally found under the topic "Steam integration not showing owned games" Post is on page 5.

That doesn't really solve the problem. You have to reconnect after every restart of GoG Galaxy and read the game catalog again.

Well until GOG bothers to fix it, its the best I've got.

I recommend Playnite or Launchbox

Updated fix. I have logged out of Gog Galaxy and back into it again. Restarted the computer to. And the Galaxy connects to steam without issues. Thus far.

Close Gog Galaxy.

Go to https://github.com/ABaumher/galaxy-integration-steam/releases/tag/Beta
and download the files.

Delete the files in the folder
"%LOCALAPPDATA%\GOG.com\Galaxy\plugins\installed\steam_ca27391f-2675-49b1-92c0-896d43afa4f8" folder.
To make life easier do not delete the folder itself.


Extract into the above folder and restart.

thanks it's an ok fix for now. Hopefully achievement tracking etc. will carry on.

I tried this solution, but my Gog folder doesn't had nothing associated with steam, only GalaxyPluginEpic and for Xbox, can you help me with a video, maybe I will figured out?