I didn't add it to any lists, but to the network interface itself. You know the output of ip a? The one pihole listens on (wg0 in my case, because wireguard) has something like, say, 10.0.0.1, but also8.8.8.8. So when a DNS packet is spit out by chromecast to go to 8.8.8.8 UDP port 53 - my pihole happily answers that request. You could also do a separate unbound instance on a new virtual interface with a quad8 ip and just forward everything to pihole, if you fancy.