I'll add myself to the list of people experiencing issues. I'm not much of a Mac gamer, but I recently bought a MacBook Air M3 and was curious if it could run Pathfinder: Path of the Righteous. I picked up that game and Legend of Grimrock on sale.
The latter has some issues on Mac as it is; when you touch the settings, it saves the string 'nil' in its config file as the screen resolution to use, which stops the game from launching entirely. Luckily that can be fixed by updating the config file and setting the resolution manually. With all my attempts getting the game to run, I also closed and relaunched the Galaxy app a few times. Or so I thought. It was running twice at some point, which caused a weird issue in Legend of Grimrock where I had to double click menu options for them to work, and interacting with items in the world downright didn't work. A single click did nothing, a double click picked something up and immediately put it down again. So not only is it messing up macOS processes and hogging CPU, it's also messing with the games it launches. That click issue was immediately resolved when I had force quit everything GOG-related.
I guess I'll just delete Galaxy and download the game installers from the website instead?