Downgrading Grand Theft Auto V from 1.0.2189.0 to 1.0.2060.1 on the Epic Games Store involves replacing the game's executable files, update.rpf , and associated metadata with older versions to ensure compatibility with specific mods. This process, as outlined by HakuX on Just Game On, requires utilizing a "No Launcher" or custom launcher method to prevent the Epic Games Store from automatically updating the game back to the latest version. You can read the full guide on Just Game On.