EdrinFr: Thanks for you attempts at helping me. But, as it happens, I'm not that ignorant. I would have liked it better if paladin was not so mindlessly aggressive, though.
To answer you, Galaxy is the problem, and steam does not support Galaxy, as it is the other way around, thank you.
I came here through galaxy interface. And Galaxy show all my previous steam games. Maybe I should have made the precision, but after having navigated through numerous very random "answers to my question" items I ended up here. I thought it was Galaxy related, not just GOG.
But I searched some more in galaxy, and found that the "connect to platform" buttons worked again. I had to reconnect steam. Until now, I thought they didn't work just because they were already connected. My library is up to date again. I just hope I don't have to connect too often in the future, and that at least, I will get a message about the need to reconnect or something.
Well, That was information that would have been helpful in helping you. I was not aggressive but genuinely confused. I click on these posts to help people, but you gave almost no detail except your Steam games aren't showing up in your library. That really sounds like a Steam issue until you add important details. We aren't mind readers friend. I hope you find your solution.