Running a Qt application on wayland works under non-qt compositors (tested with Weston and Gnome), with these environment variables :

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=wayland-egl

It also works with a QtWayland compositor, if the compositor has been run with these environment variables :

QSG_RHI_BACKEND=opengl
QT_QPA_PLATFORM=eglfs

But whenever I try to get a vulkan-only system, by starting the compositor with :

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=vkkhrdisplay

Any vulkan application simply crashes (see logs below).

To sum up, the only compatible possibilities are :

Compositor

QSG_RHI_BACKEND=opengl
QT_QPA_PLATFORM=eglfs

Application

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=wayland-egl

Or

Compositor

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=vkkhrdisplay

Application

QSG_RHI_BACKEND=opengl
QT_QPA_PLATFORM=wayland-egl

While my goal is to achieve :

Compositor

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=vkkhrdisplay

Application

QSG_RHI_BACKEND=vulkan
QT_QPA_PLATFORM=wayland-egl

LOGS (QSG_INFO=1)

qt.scenegraph.general: Using QRhi with backend Vulkan
Graphics API debug/validation layers: 0
QRhi profiling and debug markers: 0
Shader/pipeline cache collection: 0
qt.scenegraph.general: threaded render loop
qt.scenegraph.general: Using sg animation driver
qt.scenegraph.general: Animation Driver: using vsync: 16.67 ms
qt.scenegraph.general: Using sg animation driver
qt.scenegraph.general: Animation Driver: using vsync: 16.67 ms
qt.scenegraph.general: Requesting Vulkan API 1.2 Instance-level version was reported as 1.2.194
qt.rhi.general: Physical device 0: 'AMD RADV RENOIR' 21.2.4 (api 1.2.182 vendor 0x1002 device 0x1636 type 1)
qt.rhi.general: using this physical device
qt.rhi.general: queue family 0: flags=0xf count=1
qt.rhi.general: queue family 1: flags=0xe count=4
No graphics (or no graphics+present) queue family found
Failed to create RHI (backend 1)
Failed to create QRhi on the render thread; scenegraph is not functional
Failed to initialize graphics backend for Vulkan.