Elden Ring concentrates multiple characters in a single profile-level .sl2 container, so the practical backup unit is the whole account folder, not one character slot. The nearby .bak file is useful as a possible recovery point but should itself be backed up before experimentation. Because Steam Cloud can synchronize the same profile, restoration should be deliberate: close the game, preserve current local files, decide which copy is authoritative, then allow cloud sync to resume.
For this PC reference, the documented storage is Windows: %APPDATA%EldenRing<user-id> | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/1245620/pfx/. The known file or folder pattern is ER0000.sl2
ER0000.sl2.bak. The Steam PC profile uses an account-ID folder and the main ER0000.sl2 container. The .bak companion can provide an additional recovery point, but it should be copied before trying to restore it.
Backup guidance: Copy ER0000.sl2 and its .bak companion with the game closed. For maximum safety, copy the entire account-ID folder to a dated backup outside AppData. Steam Cloud is documented. Launcher and cloud context matters because The account-ID subfolder is part of the save context. Avoid mixing files between Steam identities without a tool explicitly designed for that purpose.
Compatibility and recovery should stay conservative. Save files can contain multiple characters and account-specific data. Do not treat an individual character as a standalone file. If the expected progress is not visible, If a manual restore is immediately replaced, pause and inspect Steam Cloud synchronization instead of repeatedly overwriting the live folder. Preserve both local and cloud versions until you know which one is newer. 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.