Because steam_api.dll (especially in unofficial versions) is often flagged as a false positive, your antivirus may have moved it to quarantine. Open your antivirus or Windows Defender. Navigate to the or Protection History section. If you find steam_api.dll , select it and choose Restore .

Managing connection to game servers and multiplayer matchmaking. How to Fix the Missing Steam_api.dll File 1. Check Antivirus Quarantine

Enabling achievements, cloud saves, and the in-game overlay.