The relay doesn't learn the content because it's not encrypted for it. The target receives the payload from the relay, so it doesn't know its IP, and everything the relayed removed.
Correct, we developed Oblivious DNS (first as a research paper and then as a service) to do this. Here's a quick writeup we did about our alpha service that we're planning to roll out globally:
The relay doesn't learn the content because it's not encrypted for it. The target receives the payload from the relay, so it doesn't know its IP, and everything the relayed removed.