Sekiro uses one profile-level S0000.sl2 file, so a file replacement can roll back several in-game slots at once. The safest routine is therefore simple but strict: close the game, copy the whole account-ID directory, keep more than one dated generation, and only then experiment. Steam Cloud is another revision source; if a manual restore appears to revert itself, solve the synchronization conflict before overwriting the folder again.
For this PC reference, the documented storage is Windows: %APPDATA%Sekiro<user-id>S0000.sl2 | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/814380/pfx/. The known file or folder pattern is S0000.sl2. The Steam PC profile is a single S0000.sl2 container under an account-ID directory. Multiple in-game slots are not separate operating-system files.
Backup guidance: Copy the entire Sekiro account-ID folder with the game closed. Keep multiple dated versions because the game continually updates the same container. Steam Cloud is documented. Launcher and cloud context matters because The user-ID directory is part of the save context. Do not assume a copied S0000.sl2 belongs to the active Steam identity.
Compatibility and recovery should stay conservative. One .sl2 container can hold multiple in-game slots. File-level replacement rolls back the profile container, not one isolated character slot. If the expected progress is not visible, If a restore is replaced on launch, compare Steam Cloud state and modification times. Keep the original local file before testing any imported container. SaveEditor.com only labels a game-specific editor as available when a separate linked Tool has a verified operational runtime; this reference page by itself is not an editor claim.