Restrict Whonix-based qube to selected website/host?

[qubist]

I have been using it for a long time:

[guide] how-to setup a sys-dns qube

The firewall documentation says: “Qubes does not support running any networking services (e.g. VPN, local DNS server, IPS, …) directly in a qube that is used to run the Qubes firewall service (usually sys-firewall) for good reasons. In particular, if you want to ensure proper functioning of the Qubes firewall, you should not tinker with iptables or nftables rules in such qubes.” which sounds confusing because: sys-firewall is not a service, it is a VM the “good reasons” have not been expl…

That is for clearnet though.
For Whonix I still don’t know what to do.