I think that message just means the ICD loader tried the NVK driver before trying the proprietary driver, and it’s safe to ignore. To actually silence it, you can set the environment variable VK_DRIVER_FILES. I have this in my NixOS config:
environment.sessionVariables.VK_DRIVER_FILES = "/run/opengl-driver/share/vulkan/icd.d/nvidia_icd.x86_64.json";
If you also have integrated graphics (such as on a laptop), you will want to set that to a colon-separated list of all the driver files for your GPUs, otherwise Vulkan will never work on your other GPU(s).