And then on the gaming rig it says to connect a hdmi cable from the rig to the hd60 “IN” port. After that the video says to download OBS on the gaming rig , make a source choose display capture, then right click and project to the
That doesn't make any sense, anything you connect to the HDMI IN port on the elgato is automatically processed by the elgato.
If you don't use your main HDMI cable that is plugged into your monitor you will have to tell your GPU to duplicate everything on the other hdmi as well. (It's called dual monitor/multiple displays )
But you should connect your GPU to the IN port and then your monitor to the OUT port so you always see the same thing the elgato sees.
Then connect the usb3 port to the second PC...