Animaitor: I use GOG Galaxy, I have no problem with that but cloud save is still not implemented here for some reason. I don't see the incompatibility of using a DRM free platform and having cloud saves. I have lots of games in GOG that support this feature.
The incompatibility of DRM free and having a sign in to use certain features is inherently incompatible imo. I'm not saying cloud saves are wrong, in fact they work fine on GoG if you ok with being signed into a service.
But at the end of the day it's on Terraria developers to implement it and not GoG.