I have my router (opnsense) redirect all DNS requests to pihole/adguardhome. AdGuard home is easier for this since you can have it redirect wildcard *.local.domain while pihole wants every single one individually (uptime.local.domain, dockage.local.domain). With that combo of router not letting DNS out to upstream servers and my local DNS servers set up to redirect *.local.domain to the correct location(s), my DNS requests inside my local network never get out where an upstream DNS can tell you to kick rocks.

I combined the above with a (hella cheap for 10yr) paid domain, wildcard certified the domain without exposure to the wan (no ip recorded, but accepted by devices), and have all *.local.domain requests redirect to a single server caddy instance that does the final redirecting to specific services.

I’m not fully sure what you’ve got cooking but I hope typing out what works for me can help you figure it out on your end! Basically the router doesn’t let anything DNS get by to be fucked with by the ISP.