So I have a fresh install of Windows 10 (1803) running an AMD FX 8350, 8GB of Memory and a RX 560 (Driver 126.96.36.199). I have installed Adobe Premier and Media Encoder (updated to latest) and the Mercury Playback Engine is stuck on Software and greyed out.
I ran GPU sniffer and got the attached so I am not sure what is happening, it's like the GPU is not being detected at all. Something to note is I installed Adobe to the D: drive as the system drive is a small SSD.
I had seen this but given this was a fresh Windows install I figured it should be fine, but alas, used DDU to remove the driver and reinstalled and now it's working.