I opened a ticket to support and they told me this:
It appears that the app itself is unable to determine the reason for the cloud sync failure. However, a different log file tells us more about the issue at hand.
2025-03-21 00:35:21.890 [Error][ (0)] [TID 8792][comm_service]: [CloudStorageCompressingClient::GetFilesMetadataListener] Failed to get files metadata
2025-03-21 00:35:21.890 [Warning][ (0)] [TID 8792][comm_service]: [DownloadRemoteFilesMetadataOperation] OnGetFilesMetadataFailure: Failed to get files metadata from the backend; failureReason=0
These error messages suggest that GOG GALAXY is unable to establish safe connection.

Please add the following files to both your antivirus and firewall trusted/exception list:
C:\Program Files (x86)\GOG GALAXY\GalaxyClient.exe
C:\Program Files (x86)\GOG GALAXY\GalaxyClientService.exe
C:\ProgramData\GOG.com\Galaxy\redists\GalaxyCommunication.exe
C:\ProgramData\GOG.com\Galaxy\redists\GalaxyUpdater.exe
Make sure to restart GOG GALAXY after following above.

If you have already whitelisted GOG GALAXY files, the "Scan secure connection" option enabled in your security software may be causing this issue, this option can also be called scan SSL/TLS connections - please make sure to disable it.

If you are using any kind of download boosters or network managers, please shut them down as well and let me know if the problem will persist

Let's see if it solves it but I think it's a software problem since it doesn't happen with version 2.0.74.352.