If you want to use two Elgato USB 3.0 Devices on one computer at the same time, your computer will need to have two separate USB 3.0 Root Hubs or Host Controllers.

Elgato USB 3.0 Devices include:

Elgato Cam Link

Elgato Cam Link 4K

Elgato Game Capture HD60 S

Elgato Game Capture HD60 S+

Elgato Game Capture HD60 X

Elgato Game Capture 4K60 S+

Elgato Game Capture 4K X

Not every Desktop computer has two separate USB 3.0 Root Hubs.

Many Laptop computers do not have two separate USB 3.0 Root Hubs.

The following article discussed where you can find out how many USB 3.0 Root Hubs your computer has.

 

PCs and USB 3.0 Root Hubs

You can use the Device Manager application on your Windows PC to find how how many USB Root Hubs are installed, and whether they use USB 2.0 or USB 3.0.

To find the USB Root Hubs:

1) Open Device Manager
2) Switch the view to "Devices by connection"
3) Expand all of the PCI Express entries to find the USB Root Hubs

Here is an example screenshot showing a PC with two separate USB 3.0 Root Hubs and a Cam Link 4K attached to each one:
 

Alternatively, you can use the free USBtreeview utility to examine your PC to find information about USB Root Hubs:
 

http://www.uwe-sieber.de/usbtreeview.html

Macs and USB 3.0 Root Hubs

You can use the System Information application on your Mac to find how how many USB Root Hubs are installed, and whether they use USB 2.0 or USB 3.0.

Here is an example screenshot showing a Mac with two separate USB 3.0 Root Hubs and a Cam Link 4K attached to each one:
 

Here is an example screenshot showing a Mac with two separate USB 3.0 Root Hubs, but two Cam Link 4K units are attached to only one USB 3.0 Root Hub.  This will cause problems, or not work at all:

 

Here is an example screenshot showing a Mac with only one USB 3.0 Root Hub.  Only one Cam Link 4K or other Elgato USB 3.0 Device can be attached: