Users who clone whonix-gw or whonix-ws, will quite likely either not know they have to edit
/etc/qubes-rpc/policy/qubes.UpdateProxy or forget about it.
I am not sure what @marmarek will decide wrt https://github.com/QubesOS/qubes-issues/issues/3118 and when the solution flows into Qubes.
Meanwhile I would like to add a workaround. Please check the implementation.