This should actually be posted under "Ideas" (the official feature request channel).
It has never been possible to choose GPU in Photoshop, and considering that Photoshop tends to choke on more than one GPU, that would solve a lot of user issues. They fall in two groups: One, laptops with integrated GPU in addition to dedicated card, and two, people who do advanced 3D and video who need the power of multiple GPUs.
The way Photoshop works cannot take advantage of more than one GPU, since data go back and forth. That's fine, and one is enough. The question is what to do when the other gets in the way.
It would be very interesting to hear the technical explanation why this isn't possible. Adobe are well aware of the problem, which is frequently reported, and since it's still not possible to choose, there has to be a technical reason. Otherwise it would have been implemented a long time ago. The only official remedy is to completely disable the "offending" GPU.
Perhaps there simply aren't any APIs available in Windows or MacOS to do it.