Adding some context since I stumbled upon this thread looking for the same non existing domain:
The platform this appears on is Google Discover. It's native on android, available via the google app on iOS and desktop in some countries. It's a recommendation engine that learns about the user interests and (aims to) suggest the best fit.
AIGC is indeed an acronym for AI generated content. We already saw AI overviews on Discover, where several news were grouped under a cluster. This also happens on Google news.
Here, it seems like a Google experiment (or rather bug) where they used an internal or virtual domain, discover.aigc, that the devices can't resolve.
This domain appeared on Discover (and many different locales) days ago, and more concerning, is gaining visibility fast. It's now a few percent of the visibility, which is really a lot in terms of absolute numbers.
Disclosure: I work for a service that monitors Google Discover, why I saw this domain rising and dug. We wrote a first article here https://1492.vision/experiments/discover.aigc?lng=en with a bit more data, now waiting to see how long Google will take to fix it and what is supposed to be delivered behind that link (my take: a list of real publishers cards)