The save location depends on your game launcher and Windows version.
If you can't find the AppData folder, go to your File Explorer settings and check "Show hidden files, folders, and drives." Conclusion The save location depends on your game launcher
This happens if the save file version does not match your game version. Since the game lacks a native level-select feature
For players of Prince of Persia: The Forgotten Sands , level-wise savegame files are a community-driven solution to the game's restrictive and occasionally flawed progression system. Since the game lacks a native level-select feature and relies on a rigid autosave mechanic, these external save packs are highly regarded by the community. Overview of Level-Wise Savegame Files Troubleshooting Tips
If you are playing via Ubisoft Connect or Steam, disable in the settings before launching. Otherwise, the launcher may overwrite your new save files with your old ones from the cloud. Troubleshooting Tips