The steam-api64.dll file is a shared library file that is part of the Steam application programming interface. Steam is a digital distribution platform developed by Valve Corporation, and the Steam API is used by game developers to integrate Steam functionality into their games. The steam-api64.dll file is specifically configured for 64-bit environments and is required for games that use Steam components, such as online co-op and achievements. Causes of the “prevented loading of file steam-api64.dll” error There are several reasons why you may encounter the “prevented loading of file steam-api64.dll” error in Arma 3:

Solution 1: Update your Steam client... - "Update your Steam client" → Upgrade your Steam client

Third part: "System file corruption: Corruption in system files, such as the Windows registry or system DLLs, can also cause the error." - "Corruption" → Decay - "System files" → System files - "cause the error" → trigger the problem