Just a note if anybody doesn’t know already:

To enable your Vulkan application to receive steam overlay support, make sure you add the Vulkan instance layer to your device initialization.

Here’s mine:

std::vector<char const *> const validationLayers = {
#ifndef NDEBUG
#ifndef Q_OS_ANDROID
    "VK_LAYER_LUNARG_standard_validation",
#else
    "VK_LAYER_GOOGLE_threading",
    "VK_LAYER_LUNARG_parameter_validation",
    "VK_LAYER_LUNARG_device_limits",
    "VK_LAYER_LUNARG_object_tracker",
    "VK_LAYER_LUNARG_image",
    "VK_LAYER_LUNARG_core_validation",
    "VK_LAYER_LUNARG_swapchain",
    "VK_LAYER_GOOGLE_unique_objects",
#endif
#endif
    "VK_LAYER_VALVE_steam_overlay_64",
    "VK_LAYER_VALVE_steam_overlay_32",
};