Welcome.
iptables rules in qubes always give me a headache, with that weird DNS and DHCP setup and considering there’s also nftables and you don’t know which takes priority… so you end up duplicating your efforts in both iptables and nftables just to be sure…
After some searching found some clarification about the whole iptables-nftables business
Still doesn’t answer what happens when you set contradictory rules using both commands.
Also even after trying reading docs multiple times still can’t wrap my head around that PR-QBS DNS propagation business. In general my confusion stems from DHCP server sitting somewhere (as I understand it) in the back of qubes infrastructure and communicating with vms in mysterious (to me) ways (qrexec?), and the whole DNS business communication being facilitated by interacting with something in the back of qubes using qubes specific mechanisms but wrapping them in the standard network protocol clothes, ergo the whole PR-QBS chain in the table…
anyway… for what you want you would need to route from your vpn vm tun interface to your kali
you could try instructions here in the section Port forwarding to a qube from the outside world
for openvpn setup I recommend using qubes-tunnel