Here is the fix, ranked from the most likely solution to the least.
The Fix: Right-click the OneDrive icon in your taskbar, go to Settings, and under the "Backup" or "Sync and backup" tab, click Manage Backup. Toggle off the "Documents" folder.
Root causes (most common)
The game often struggles with special characters or non-English paths.
If absolutely nothing works, you can use a 100% clean save file from the internet.