SargonAelther: And you want Galaxy to make that determination?
joppo: Of course not! Where did you get that idea from?
This is not something that should be determined by Galaxy at the time the user is playing the game, but by a Gog employee at the time the game is accepted into the store,
long before it is put up for sale. Exactly for the reasons you stated.
Thus when the game is being prepared for sale a Gog employee would record ONCE in which folder the game stores its savefiles. Later when Galaxy decides it is time or is prompted to sync saves with the cloud it can retrieve that config and know directly what folder to sync for that game. No fussing around in your PC needed at all.
Well you sentence contained no agent in your reply to me, asking how would "Galaxy" know, so I assumed you meant Galaxy itself as the agent of that determination action, rather than an employee of GOG. I could not have known what you meant exactly any more than a person who received a simple "Yes" as an answer to his question of "Would you like some apple juice or some orange juice"?
Anyway, yes, a GOG employee could do this, that's true, but I would not be surprised if there is a lot of bureaucracy involved in such things and GOG cannot intervene, either legally or ethically.
Personally, I don't use cloud saves anyway, 'cause they always seem to cause more problem than they solve, but I have very specific use cases, so I'm not a target audience for cloud saves to begin with.