I've faced this issue on all my Android phones across various Android versions.
When I have NextDNS enabled as my private DNS, my phone isn't able to communicate with my dashcam (Yi Nightscape). I can join the WiFi connection created by the dashcam but the dashcam's app isn't able to connect to the dashcam. I have to go into the settings and turn off Private DNS, then remember to turn it back on once I'm done.
Nothing shows up in the logs for me to allowlist, and I can't seem much information regarding it online as well. I don't think NextDNS even has a pause button to temporarily disable it.
I don't have knowledge about networking to even know how to troubleshoot, or whether I'm even describing the issue properly. I was hoping someone with more insight could help me with this.
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.