I have installed Rx580 (gift from a friend) after having an APU for a year... and I thought I'd be able to use the feature but I still can't. And I have already done everything I read on any technical support I could find but it still wont work.
I have uninstall/reinstalled driver, disabled windows update, used DDU/AMD Cleaner, and even installed Older Versions.
My guess is that the APU is preventing the software from installing it.
But I dont know any way to install only the GPU Driver since the installer would detect both devices (though I would like to have both drivers installed for backup if the GPU stopped working one day)
I only want to have the feature so I could use AMD Link and play my games on couch or bed.
Disable the amd apu graphics, download/install the RX580 driver package direct from AMD.
You also might look in the bios for a option to select the 'Primary' graphics and choose the 580.