It still needs the Elgato Master Mount L ... which is unfortunately not available at the moment ... but you can also buy the Elgato Key light or Key light mini ... the base and holder are already included ... and you can also mount the extensions.

If you don't need it so big, you can also buy the solid arm, which works just as well. Only with the multimount l and the solid arm is the part with the screw for the camera included.

If you have the following product Elgato Master Mount L you can already install the camera, the Multi Mount is simply meant to extend the standard product to achieve e.g. 90° angles, etc. I hope I could help.