If vulkan doesn't work correctly, vulkan apps are crashing or you're getting "lavapipe is not a conformant Vulkan implementation, testing use only" in the terminal when launching vulkan apps, you've probably hit upon this issue.
Not quite sure where this problem actually comes from, but something is making the vulkan libraries load the software renderer, "lavapipe", instead of the nvidia accelerated driver.
A workaround is to set the environment variable
VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/nvidia_icd.json. You can either
export VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/nvidia_icd.json in a terminal
and launch vulkan apps from there, or add
VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/nvidia_icd.json to
/etc/environment (requires a relogin or reboot).