Often devices will have the DNS server hard-coded and never connect to the pihole DNS server. This is not just to avoid ad-blocking but to make the DNS more reliable and avoiding having lots of potential support issues around faulty DNS.
I've never used pihole, but on any decent router you can intercept outgoing udp to port 53, and redirect it to a destination of your choosing. DNS-over-HTTP ruined that however.
encom|2 months ago