My current setup is a 2 GPU setup, with an RX 480 as primary and a GTX 960 as secondary. I used to run nouveau just fine, X detected it and I could connect monitors or offload workloads onto it with prime just fine. But then i started coding vulkan, and saw that vulkan is not supported by nouveau. So I had to install the proprietary driver for this. But now, my second GPU is just straight up invisible to X. I have tried any xorg.conf ever, always nothing, as if it wasn't there. Kernel driver works perfectly fine though, I can probe the GPU, get its data, no problem; but anything involving X is just a big no.
Did I miss something? Does this require some obscure config that doesn't exist on the internet? Or is this setup just straight up unsupported?