Howtoforge published a tutorial about setup a local DNS resolver using Dnsmasq on Ubuntu 20.04.
How to Setup Local DNS Resolver using Dnsmasq on Ubuntu 20.04
Dnsmasq stands for short for DNS masquerade is a simple, lightweight and easy to use DNS forwarder used for a small network.
How to Setup Local DNS Resolver using Dnsmasq on Ubuntu 20.04