18.104.22.168 fixed itQuad9 is known to block some domains on their server's side. Try the "unsecured" addresses which don't block any domains. Hopefully AG Home switches to the "unsecured" Quad9 in the next major update, since it can do all the blocking on its side.
We're happy to announce Quad9 now has support for DNS over HTTPS (aka DoH). Want to test out Quad9? Use https://dns.quad9.net/dns-query or https://dns.quad9.net/dns-query? depending on your client.www.quad9.net
The addresses are