I noticed that if I block 8.8.8.8 from google assistants and advertise (via IPv4 and IPv6) that they wait 5 seconds for 8.8.8.8 to fail, then retry on the local DNS server. So when you say "ok google, what's the temperature?" you get an annoying 5 second delay.
Frustrating that google assistants ignore the DNS server presented to them.
If they don't use DoT/DoH, you can try redirecting traffic for 8.8.8.8:53 to your own DNS server with one or two firewall rules. If they're actually securing the connection that won't work, though.
Indeed. I block port 853 and various popular DoH servers and then rewrite any port 53 access to use my servers. So far it's working well. Frustrating that so many devices ignore DHCP (IPv4) and RADVD (IPv6) recommended name servers.
Frustrating that google assistants ignore the DNS server presented to them.