Windows Mixed Reality Ultra PCs
NVIDIA GTX 960/1050 (or greater) DX12-capable discrete GPU
AMD RX 460/560 (or greater) DX12-capable discrete GPU
GPU must be hosted in a PCIe 3.0 x4+ Link slot Integrated Intel® HD Graphics 620 (or greater)
Windows Mixed Reality PCs
DX12-capable integrated GPU (check if your model is greater)
NVIDIA MX150/965M (or greater) DX12-capable discrete GPU
Where does the spec say that your 7850 should be capable of running this?
It doesn't meet the requirements for an "ultra" Pc, and your entire manufaturer isn't listed for the non-ultra option.
This is a comparison of your card, the (high)mid-range card from 2010 I recently gave away for free, and my current (compatiable) card.
The 7850 is underpowered and not compatiable, and almost 6 years old, predating the occulus rift kickstarter. Note that it only supports DirectX 11.2
Sorry to burst your bubble, but it was never going to be enough for VR, as VR needs more grunt.