Sometimes, antivirus software can mistakenly block or delete game files or DLLs. Temporarily disabling your antivirus to see if it resolves the issue can be a troubleshooting step, but remember to re-enable it for security.
For Windows, you can use the System File Checker tool to repair corrupted system files. call of duty infinite warfare steam-api64r.dll missing
Sometimes Steam itself breaks.
Steps:
When Call of Duty: Infinite Warfare downloads a patch, the Steam client verifies existing files. If your internet connection drops or your hard drive has bad sectors, the steam-api64r.dll file can become corrupted or partially downloaded. Sometimes, antivirus software can mistakenly block or delete