IW6x should support xbox controllers out of the box. If it does not work, make sure "Gamepad Support" is enabled in settings.
- Download DS4Windows, make sure you pick DS4Windows_xxx_x64.zip
- Install/Extract it to a safe place and open it.
- It should detect your controller, but if it does not, you may need to install the driver.
- Check if gamepad works in IW6x. If there is still problems, you can join the Discord and ask for support in the #iw6x-support channel.