I don’t know how the others set theirs up, but I use “views” in bind 9 kb.isc.org/docs/aa-00851

Essentially, the DNS I run on a router-like box much like you describe uses a different database depending on whether you query from an internal IP address or a public address. For me, the advantages are that I can let devices on my local network declare their own names to DHCP and enter them in DNS without worrying about the outside world. Mu internal network doesn’t crash if my ISP changes my address, Certbot happily requests certs for any site with a public address, and that cert works seamlessly on the corresponding internal address, no wildcards or DNS challenge required.