Every Microsoft operating system since Windows 98 can be affected by d3d9.dll and other DirectX issues. This includes Windows 11, Windows 10, Windows 8, etc.

Follow these steps in the order they are listed below to try the simpler solutions first.

Restart your computer if you haven't already. The error could be a fluke and a simple restart could fix it completely.

Install the latest version of Microsoft DirectX. There is a good chance that upgrading to the latest version of DirectX will resolve the d3d9.dll not found error.