Download the 6.0 RC and try building one of the Vulkan-based examples in qtbase with qmake:
whereas CMake works as expected.
With qmake it seems that the -IC:\VulkanSDK\22.214.171.124\Include argument goes missing. (it should be generated based on the VULKAN_SDK environment variable, which is set to C:\VulkanSDK\126.96.36.199 on my system)
Same goes for the Qt Quick examples that use Vulkan directly (vulkanunderqml, vulkantextureimport): they end up in: