Open the file /etc/default/grub in dom0.
Find the line that begins with GRUB_CMDLINE_LINUX.
Add usbcore.authorized_default=0 to that line.
Save and close the file.
Run the command grub2-mkconfig -o /boot/grub2/grub.cfg (legacy boot) or grub2-mkconfig -o /boot/efi/EFI/qubes/grub.cfg (EFI) in dom0.
It’s not clear from the “Qubes 4.1 only” note at the end of “How to create a USB qube for use with a USB keyboard” that the referred to setting of usbcore.authorized_default is in relation to section “How to enable a USB keyboard on a separate USB controller” which I don’t need.
@disp6252 has pointed you to the correct procedure.
Indeed, from my reading, I do not see where your confusion comes from.
But now that you do know the right thing to do, you should be able to
suggest an improvement that would not lead to the confusion you had.
I never presume to speak for the Qubes team.
When I comment in the Forum or in the mailing lists I speak for myself.