If you don’t know Elgato Cam Link 4k it is transforming any HDMI device into a webcam and you can capture or stream from it. Elgato Cam Link 4k it is an adaptor that is plugged into your PC thru a USB3 and your camera thru HDMI and it is converting it to a webcam. You need to connect it to USB 3.0 at least to have the necessary transfer rate.
Elgato Cam Link 4 it is relaying onto your PC/Laptop hardware to do the transcoding. You need a really good computer so it can work properly. You need a minimum Intel i5-4th generation CPU in order to function properly. With the proper hardware, it can record 4k videos. Also is working with Windows and Mac.
Elgato software is not that good as it is using a lot of resources and you better use a 3rd party software to record your camera with Elgato.
There is a very interesting video with Elgato Cam Link 4k Review done by Lon.tv where it is testing it and see exactly how is doing. Watch the video to see what exactly Elgato Cam Link 4k has to offer.