JakobFel: I haven't used Minigalaxy much at all so far (mostly because my experience with Linux is merely experimental until next year) but it seems viable. So far, Lutris seems to be the best option overall, especially since it offers similar functionality to GOG in that it's an all-in-one launcher. I haven't tried Heroic but it's definitely on my radar.
Supervisor360: problem with them is that many gog multiplayer games use goggalaxy specifically to play multiplayer.
Yes, that's problematic but I can't really see another way for games if they're not built specifically to be DRM-free releases. Everyone uses Steamworks for multiplayer these days, so GOG needed a competitive option. Unfortunately, that results in this issue.