Virtualmin is configured to setup DNS zones, but this system is not setup to use itself as a DNS server. Either add 127.0.0.1 to the list of DNS servers, or turn off the BIND feature on the Features and Plugins page. It appears that DHCP is being used to dynamically configure your network interfaces, which can cause the DNS servers to be set based on settings provided by the DHCP server. Using a static IP address is strongly recommended with Virtualmin.
This is on a local SOHO, off the Internet with currently no plans to host anything that Internet can reach so what should I do?
(Well, I will install some monitoring stuff like nagios or Matomo I use to check/backup some websites (SFTP), but I don’t think that counts.)