Galaxy 2.0 Game Library shows game clients all but GOG... am I missing something?

EDIT:

OK, so I see you can set up bookmarks.

And also filter. But filter doesn't work right. I filter by "Installed" and "Gog.com" but it still shows games in Steam.

I think if the game is available and installed on Steam, but not on Gog.com it still shows it as a gog.com game.

Here's video: https://youtu.be/QjrsBDSxYpo

In the video, there's an icon that has the number "2" at the top of your screen. There, you can select on which platform/launcher you want to launch the game from. My guess is the same as yours, that it defaults to the platform that you have it downloaded for.