The file is a metadata file used by the Steam client to track the installation, update status, and configuration of Hello Neighbor 2 (AppID 1173510). Purpose and Function
: If this file is missing or corrupted, Steam will show the game as "uninstalled" in your library, even if all the actual game data remains in your common folder. appmanifest_1173510.acf
: These .acf files (Valve KeyValues format) serve as a "map" for Steam. They tell the client that a specific game is installed, where its files are located, and what version is currently on your disk. The file is a metadata file used by