It seems to be related to the app store and os updates. All my apple devices attempt to connect to it during updates. On MacOS the processes which attempt connection are commerce, appstoreagent, rtcreportingd and App Store.
I would speculate that it is for some kind of telemetry, as I have had it blocked for a couple of months now and it has never caused ...
I've been having this problem myself recently. What just happened to work for me (after already attempting restarts, dns flushes, dns server changes) is to disable Content Caching. Content Caching can be found in System Settings ➡︎ Sharing.
After this the update started to download immediately.
Yes, it frustrates me too, but I'm afraid that there is no easy way to accomplish what you need. Possible workarounds I found are:
use a proper domain name, preferably the one you already own. From my experience, this is a common practice, instead of using made-up TLDs.
use Firefox, which attempts to resolve custom TLDs.