I'm playing Divinity: Original Sin 2 Definitive Edition in GOG and the game always cloud-syncs, but I don't want it to. I turned off cloud sync in both the in-game settings and GOG Galaxy's global settings. But the game still always syncs when I exit the game. And it takes a long time to cloud-sync because the saved games have big file sizes. Is there any way to disable cloud sync for good? Is this an issue with the game or GOG Galaxy?

Sorry cannot answer your question but here two things that may or may not be of slight help:

Galaxy's own subforum: https://www.gog.com/forum/general_beta_gog_galaxy_2.0

The client is not needed at all in order to play the games here, some multi-player excepted.

.
.
.

I did post there, but not many people visit there. I also posted at the Larian Studios forum, but you hear crickets there too. The General Discussion forum is the only GOG-related place that is swamped with people, so I thought I had better chance here. Here is a screenshot, btw: https://i.imgur.com/W9Jryvg.jpg . I have cloud sync disabled globally but the game (ANY game, in fact) still tries to cloud sync. Here is a video capture of what happened: https://www.youtube.com/watch?v=Sm13TRSeK_w. And yes, I've submitted a ticket to GOG support too. This doesn't seem to be a common problem. I've googled and found nothing.

If you exit Galaxy, really exit...not just send it to systray and then restart it is the setting still turned off?

.
.
I have restarted GOG Galaxy and my PC many times, turned the cloud sync setting on and off many times, and the settings in GOG Galaxy are always what I set them to be, so no issue there. The problem is that it always cloud syncs even if the cloud sync setting is off. I've since reinstalled GOG Galaxy, and the problem is still there. I googled, and found no one else with this problem. As my video capture above shows, I'm not seeing things here. The only thing I haven't tried is reinstalling DOS2, but it's a 2-hour download.

Yes. Uninstall GOG Bloatw.. Galaxy. Properly. Possibly nuke the computer to get rid of the remains.

Sometimes the simplest solution is the best. If you don't want client features, then you don't need to use the client...

.
.
.
I do need the features in GOG Galaxy in order to organize my games.

I uninstalled and reinstalled the game, and the problem still occurs. I'm really out of ideas now. And GOG support hasn't responded with any solution.

The saved game files are 5 megabytes each for this game, and my upload speed is only 5 megabits per second = 0.625 megabytes per second. So it takes over A MINUTE to sync only 10 saved games. That's the main reason I want cloud sync disabled. I do want to use cloud sync. But I usually do it when I've finished the game, so I can cloud sync all saves at once.

For those who don't like client features, wait till you replay an old game and you SCRAMBLE to find your old saved games that you forgot where you put in your PC, then maybe you'll realize how valuable this is. Saved games are CONFUSING nowadays. They can be saved in a ton of different possible locations. When you upgrade your PC or hard drive, you have to SCRAMBLE to look them for all possible locations, and you may miss some. Just cloud sync ONCE when you finish the game, and you'll always have a peace of mind. And you know you'll get them back on whatever PC you use in the future.

When I want to replay an old game, I usually start playing from the beginning...

That's why I use GameSave Manager. One piece of software that works with all games (including CD-ROMs, floppy discs, etc), doesn't care where you bought them from and works without the walled garden-ness of store-locked clients.

.
.
.
Thanks! Your info definitely helped. I switched back to the default executable (SupportTool.exe) and sure enough it stopped cloud sync. The one I used before isn't custom, since it's the game's OWN executable (EoCApp.exe), which launches the game directly instead of launching the Larian launcher. I tried another game with a custom executable file, and surely, it cloud-synced even with the cloud sync setting off.

Is there any discussion threads on reddit or whatever that you can remember and give me the link for? I want to glean more info about this topic. As I said, I already contacted GOG. But it doesn't give me confidence that it will be fixed soon after what you said. Well, this is a beta after all.

Glad to help. I haven't noticed this problem being discussed anywhere but on these forums occasionally, I had just discovered it myself and submitted a bug report for it.

If you get through to a live person in support maybe the issue can get pushed to someone who can fix it.

.
.
.
I used to use tools like that in the age of physical discs. But cloud-saving today is infinitely better because it not only saves time but also gives you another insurance because your data reside in the cloud instead of locally, where data corruption, hardware damage, theft, etc. are possibilities. Cloud storage is used on so many devices and by so many users today that it may have prevented a lot of data loss among many users.

That's exactly what it does as well (see the "Cloud Options" menu). And with the option of multiple cloud services at that (DropBox, Google Drive, OneDrive, etc) for the ultimate in insurance.