Hi,

welcome to the official GOG Galaxy forum thread. Please read the below info first:

== GOG GALAXY FEATURES IN GAMES ==

List of games supporting various GOG Galaxy features:
Achievements: https://www.gog.com/games?feature=achievements&sort=bestselling&page=1
Cloud Saves: https://www.gog.com/games?feature=cloud_saves&sort=bestselling&page=1
Overlay: https://www.gog.com/games?feature=overlay&sort=bestselling&page=1

== BUG REPORTING ==

Please use: http://mantis.gog.com and include
1. steps to reproduce the bug (if possible)
2. screenshot or movie showing the bug (if possible)
3. Galaxy Client logs (location described on mantis report page)

== FEATURE SUGGESTIONS ==

Please use: http://www.gog.com/wishlist/galaxy. For feature suggestions and votes on them please try do explain how Galaxy and its users will really benefit from it.

== IMPORT ALREADY INSTALLED GAMES TO GALAXY ==

1. For GOG games installed using installers from the last few months (so called Galaxy-compatible installers)
Click the Galaxy logo button on top of the sidebar and select "scan and import folders" - it will find all compatible games within that folder and add them to the Client.

2. For remaining GOG game INSTALLATIONS
Find the game in the Library (click on the image of the game), then click the More button and select "Manage Installation" -> "Import folder" and point the folder selector into the folder where that game is installed.

== KNOWN ISSUES ==
- Galaxy cannot be launched by other users on the same computer

== CHANGELOG ==

1.2.49 (November 29, 2018)
- [Windows] Updater now requires administrator privileges to perform update of GOG Galaxy
- [Windows] Security of directories containing GOG Galaxy files has been improved
- [Windows] Updated Code Signing Certificate
- [Windows] Crash reporter has been added to Galaxy Communication Service
Bugfixes:
- Prevented several potential causes of "broken" games, where only way out was reinstalling
- [MacOS] Fixed a crash on shutdown when fatal error was shown

1.2.50 (December 13, 2018)
Changes & Improvements:
- Speed up startup time
- [MacOS] Strengthen up connection security with ClientService
Bugfixes:
- Fixed "disk access problem" when installing games, occuring mostly on fresh installation of GOG Galaxy
- Fixed a rare occurrence of a game update resulting in displaying "unknown game version"

1.2.51 (December 20, 2018)
- Improved Korean translations
- Fixed connection to notifications pusher in GOG Galaxy SDK

1.2.54 (March 14, 2019)
Changes and Improvements:
- Updated Chromium version to 71:
- Better performance
- Fixes playing Twitch videos on profiles
- Fixes playing Wistia videos
- Security fixes in the game installation process
- Security fixes in GOG Galaxy update process
- GOG Galaxy Updater should perform better under poor network conditions
Bugfixes:
- [macOS] Fixed passing multiple commandline arguments to games
- [macOS] Multiple "friend online" notifications will no longer appear when system wakes up
- Dates are now properly displayed in cloud saves conflict window

1.2.55 (April 17, 2019)
- Hotfix for unintentional opening of Facebook link after entering Forum

1.2.56 (May 06, 2019)
Bugfixes:
- [Windows] GOG Galaxy will fix the path to its internal services, if it finds it is wrong
- Updating of games' local dependencies (e.g. Dosbox) will be handled correctly
- Unexpected files in games' directories will no longer cause failure of games’ update

1.2.57 (June 12, 2019)
Changes and Improvements:
- Minor download speed optimizations
- Changes in PayPal payment flow
Bugfixes:
- Fixed rare crash occurence when reordering games' updates and installations
- GOG Galaxy will correctly reconnect to GOG services after long time of no internet connection

1.2.58 (September 13, 2019)
macOS:
- Enabled hardened runtime, making our application more secure
- Implemented Apple's notarization

1.2.59 (September 23, 2019)
Overlay:
- [Windows] Fixed crash in Overlay affecting some games (including Fallout 3 (Radeon only) and Dragon Age: Origins)
Achievements:
- [Windows] Fixed issue with achievements sometimes not being saved while playing offline

1.2.60 Beta (07 October, 2019)
General:
- Updated CEF version to 3729 (Chromium to 74)
- Security fixes
Updater:
- Will no longer download updates at startup, they will be downloaded in the background, while the application is running
- [Windows] No additional UAC prompt during update

1.2.61 Beta (October 23, 2019)
Updater:
- Fixed an issue where non-admin users would not be able to update to newer versions of GOG Galaxy

1.2.62 Beta (October 30, 2019)
Overlay:
- Fixed crashes for various games

1.2.63 (December 02, 2019)
General:
- Updated CEF version to 3729 (Chromium to 74)
- Security fixes
Updater:
- Will no longer download updates at startup, they will be downloaded in the background, while the application is running
- [Windows] No additional UAC prompt during update
Overlay [Windows]:
- Now supports games which use Vulkan API (e.g. Jupiter Hell, X4: Foundations)
- Fixes crashes for various games

1.2.64 (December 04, 2019)
- Hotfix for launching games

1.2.66 (January 23, 2020)
- Added information about GOG Galaxy 2.0 Open Beta
- Optimization related to showing download progress
- Fixed an issue where Overlay did not launch for some games that use Vulkan
- [Windows] Updated code signing certificate
- [MacOS] Crash fixes

1.2.67 (February 24, 2020)
General:
- [Windows] GOG Galaxy will now show a warning when trying to run on non-NTFS file systems
- Improved security of the application
- Updated POCO library
GOG GALAXY Update:
- Fixes for bugs in the GOG Galaxy update process

It syncs per GOG.com user. I don't know if this specific game store saves in the Documents folder. For some games it syncs also the game configs. You can always go to MORE->backups&goodies and download your cloud saves copy to check what it syncs exactly for your game. :)