The recent update to the edk2-ovmf package version 201111-4 causes a black screen when trying to install a VM. Existing VMs should boot, though. See also https://www.heiko-sieger.info/creating-a-windows-10-vm-on-the-amd-ryzen-9-3900x-using-qemu-4-0-and-vga-passthrough/#Windows_VM_Installation for workaround.
In Arch Linux this issue was fixed in release 201111-5. Unfortunately Manjaro still hasn’t updated the OVMF package. Manjaro team: please update.