One of the features that was hyped about DirectX 12 was that it had explicit support for multiple GPU's even if they were different models from different manufacturers.

As far as I know very few, if any, games currently take advantage of this feature. It's somewhat interesting that this is the case, when you think of it many PC's and laptops do have 2 GPU's, one as a Discrete Graphics card, and the other that comes integrated with the CPU itself (and over the last few year's these integrated GPU's have become powerful enough themselves to run some demanding games at low or medium settings at 60 fps)