Performing the following steps may resolve the issue.
1． Log in to Windows as a user with administrator privileges.
2． It is highly possible that the save directory cannot be written to because a file sharing service such as those below is being used:
Check whether one of the file sharing services below has been set. If so, cancel it and check if the issue is resolved.
- Google drive
- MS OneDrive
- Dropbox
3． Your saved data file may be write-protected.
Open the Properties of the saved data file or the folder where the saved data file is stored, and select the Security tab to confirm the access permissions are set correctly.
4．Confirm the Protection History of Windows Defender, and if the Documents folder is included in Protected Folders, exclude the Documents folder.
* Regarding Protection History, please refer to the following website:
https://support.microsoft.com/en-us/windows/protection-history-f1e5fd95-09b4-46d1-b8c7-1059a1e09708
5． Confirm whether the game is included in the monitoring target of the security software you are using.
Even if the game is not included in the monitoring target, try setting the game's executable file as "Exception (Exclude)" in the security software.
* Since the "exception setting" method differs depending on security software, please contact the manufacturer of the software for details.
6．Does your Windows user name include characters other than alphanumeric single-byte characters?
If it does, your data might not be saved.
In such a case, create a new user account using only alphanumeric single-byte characters and check if the issue is resolved.
Note: The issue is not related to your Steam account, but rather the username of the Windows OS.
7． Confirm if the name of "Documents" folder on Windows or the name of the folder in which "Documents" folder is stored contains 2-byte characters.
Right-click "Documents" > choose "Properties" > "Location", and see if the full path for the folder location contains 2-byte characters.
If it does, consider moving "Documents" folder into a fold that contains only 1-byte characters by clicking "Move" button.
8． PC specs: (CPU/OS/Graphic Board/DirectX Version/Memory size/HDD Free Space)
9． In Windows settings "Region and Language", make sure that the same language as the region where you live and your OS is selected.