[IPTN]

It can help with other solutions like Sunshine/Moonlight because a EDID plug advertises all the possible resolutions and refresh rate combinations under the sun so that it can be configured by the stream server to match the remote client display. Your attached monitor(s) may not support the same resolution/refresh rate as whatever client you are trying to stream to. Needing hardware for this is likely because of the graphics stack and virtualization restrictions of your graphics card if it isn't an enterprise one. Otherwise they could just use a virtual display buffer that isn't output on any screen.

All that said, I don't think steam link does this automatically, but there are probably tools that have been made for switching your main display to the dongle and setting the correct resolution for it when you initiate a streaming connection. At least I know there are helper ones for Sunshine so I am assuming it is true for Steam Link as well.

Not that this would fix an encoding issue if that is your problem.