To prevent your antivirus from deleting the file again as soon as you launch the game, you must create an exclusion.
Encountering a "Failed to load OnlineFix64.dll" error (often accompanied by or 4556 ) can be incredibly frustrating when you’re trying to launch a game. This file is a Dynamic Link Library (DLL) primarily used to bypass digital rights management (DRM) on platforms like Steam and Xbox, allowing for features like online multiplayer in modified games.
Click Add an exclusion and select the entire folder where your game is installed.