I just noticed that when I launch Forced Showdown, GalaxyCommunication.exe starts running. I hadn't noticed it before because the game had never been able to connect to Galaxy (since I never have it running), but I had briefly logged into Galaxy recently to check if the ability to turn off certain features was finally available. Despite the fact that Galaxy wasn't running, this time the game connected. I checked my processes in Task Manager, and sure enough the game had started up GalaxyCommunication.exe. I exited the game, ran Galaxy, logged out, exited Galaxy, and ran the game again. This time it was unable to connect to Galaxy like normal, though GalaxyCommunication.exe still runs in the background.

I tested this with Crypt of the Necrodancer, and sure enough that started up GalaxyCommunication.exe as well. This might explain why I had previously unlocked some Galaxy achievements for a few games even without Galaxy running. I imagine that every game with support for GOG Galaxy features does this.

I just wanted to share this information in case anyone finds it important.