Recently, my Steam integration for GOG Galaxy has completely stopped working. I've tried deleting and reinstalling the program but that still doesn't fix anything! Can someone please help me out?

Yep. same here.

At least 2 days maybe more. I have been playing GOG games in past few weeks so cant confirm when exactly.

it says after putting my details in that is offline and to retry.

I've had this happen 3 times in the past, with earlier versions of galaxy client and steam integration. At some point it simply got stuck and stopped updating no matter what I tried, so the solution for me was to unlink the steam account and reintegrate it again. After 3rd time it broke like a year ago or more, I've simply had enough and after relinking it I've removed the integration and used galaxy as gog-only client where I need it for multiplay or want it for achievements. It loads the library much faster now and it is way more responsive in general without integrations syncing and getting stuck ever so often.

Not a real solution I'm afraid, but one I can live with.

For me it always helps to close and restart Galaxy. After that I can see and play all my games. Before that all Integrations are broken and only GOG games and the ones I've added manually work.

The integration is broken and nobody is taken care of the git repo anymore:
https://github.com/FriendsOfGalaxy/galaxy-integration-steam/issues/159

So, I don't think this will just fix itself. Unless somebody jumps in, the steam integration won't work anymore. This would be bad news for GoG Galaxy, so, maybe somebody from the GoG team should jump in?