Have you tried doing it the way nvidia suggests?

https://download.nvidia.com/XFree86/Linux-x86_64/550.54.14/README/primerenderoffload.html

I do it this way on my Aurora 16x with no issue. I know nvidia has its own mechanism for selection of GPUs s that'll work with 2x nvidia

@Eckoa You are absolutely correct, for some reason filtering the device name and setting the Vulkan device causes the swapchain issue, while simply setting __NV_PRIME_RENDER_OFFLOAD=1 __VK_LAYER_NV_optimus=NVIDIA_only (without the other VKD3D options) works, but not with both.

I thought this was a VKD3D issue since DXVK does not require these specific launch parameters. Although it is only able to select the card that is first in the index, which unfortunately is my 3060. I think this is a nvidia driver limitation.

I "think" __NV_PRIME_RENDER_OFFLOAD works similar to DRI_prime In that you can select the card using it. I've seen some threads about selection of specific GPUs in multi nvidia systems around so someone knows how to do it how Nvidia expects somewhere