Why am I not getting a video stream with QEMU USB 3.0 UVC camera passthrough to a Windows 11 VM?

Setup Host: Arch Linux (Omarchy) with libvirt/QEMU Guest: Windows 11 Pro VM Device: Logitech 4K Brio (USB 3.0 superspeed UVC camera, vendor 0x046d , product 0x086b ) Problem The camera is passed through to the Windows 11 VM and recognized in Device Manager, but produces no video stream. The camera reports as in use by another application despite no other application accessing it. Audio passthrough of the webcam's microphone into the Windows 11 VM works perfectly (i.e., only the webcam video doesn't work, the webcam microphone does work). Context The same camera works flawlessly when connected

Question by Adam Mac on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.