How to send DNS lookups from Unbound through Wireguard?

[BasementDweller]

I just set up Pi-hole (I know Unbound had the same functionality now, I've just started homelabbing and am experimenting like crazy atm), and was planning to use Unbound on the Firewall itself. But, I ran into a problem : I can't find a way to direct my recursive DNS requests out of my ProtonVPN Wireguard tunnel.

I made this floating rule (that does not work, and I even don't understand why):

 - Interface: WAN
 - Direction out
 - Proto: IPv4 TCP/UDP
 - direction out
 - Source: This Firewall
 - Destin: !RFC1918
 - Port: 53 (DNS)
 - Gateway: PROTON WG

Bye, bye Internet LOL.

Has anybody tried this, because I can't find anything good on the Internets. Not knowing how is only my secondary problem. I don't have enough knwoledge to understand why it is not working. Please be kind and enlighten me. Thank you in advance!