Right, we are on the same page but from experience, setting DNS 1 to the pihole and DNS 2 to for example 8.8.8.8 in your DHCP router will make the pihole useless. There are dozens of similar threads across different forums saying the same thing but if you know how to do it please let me know… Example: https://www.reddit.com/r/pihole/comments/864oli/secondary_dns_setting/
Yeah, all I could find was vague statements about the DNS server lookup order being “OS specific” and windows specifically being know for “not respecting DNS order”, see https://www.reddit.com/r/networking/comments/kb8hvt/dhcp_dns_server_order/
This is also supported by statements from pihole devs: https://www.reddit.com/r/pihole/comments/x2248t/is_it_worth_creating_a_second_pihole_dns_server/ And: https://discourse.pi-hole.net/t/primary-vs-secondary-dns/1536/4
And then there are the hundreds of similar questions which one could take as “evidence by quantity” or whatever.