GreenLuma is a legacy tool, later succeeded by updated versions like GreenLuma 2020, GreenLuma Reborn, and GreenLuma Manager. At its core, it is a that intercepts Steam API calls. Its primary function is to trick the Steam client into believing that specific games or DLCs are already owned by the current user.
: You need "Clean Steam Files" (unmodified game data) for the game you wish to play. greenluma tutorial