Yeah this is an incompatibility issue. The two products won't work together. DNS translates a domain name to an IP address. NextDNS will have no record of the domain name the app is looking for. You've found the only solution.
Dang.
I greatly appreciate your incredibly speedy reply. Thanks!
Looking at it more, under settings there should be an option for Rewrites. If you know the name the app is looking for, you might be able to make a manual entry. This info might be in the info for the dash cam. Or you could monitor network traffic on your phone when you connect to it.
When you're on private DNS, only global (public internet) hostnames will resolve. For anything on your local network, only IP addresses will work.
There's a chance that your dashcam has its own DNS server, or registers its hostname with your router's DNS server. Either way, you'll only get the right answer from that server.
given the current state of the privacy laws, this might be a feature not a bug
Discussion about NextDNS service with ad and tracking protection.