It seems there is no way around this. Nowadays, every system has an USB mouse and keyboard plugged to the PCI. How would one install without the wireless mouse and keyboard? What would be trick to avoid creating manually the ‘sys-usb’ afterwards?
You’ll get this warning if you don’t have rd.qubes.hide_all_usb or usbcore.authorized_default=0 option in grub:
if getargbool 0 rd.qubes.hide_all_usb; then
# Select all networking and USB devices
elif ! getargbool 1 usbcore.authorized_default; then
# Select only networking devices, but enable USBguard
warn 'USB in dom0 is not restricted. Consider rd.qubes.hide_all_usb or usbcore.authorized_default=0.'