What other option do you expect there?
If you want to use USB mouse input in dom0 then you need to pass in to dom0.
Or do you want to use you USB mouse in just one specific qube that don’t have Qubes OS GUI integration (e.g. full desktop instead of seamless app windows)?
qubes.InputMouse is not attaching the USB mouse to dom0 as USB device, it’s only passing the input from the USB mouse in sys-usb to the virtual input device created in dom0.
So it’s not passing any actual USB device to dom0.
Also read this: