Yes, and Quad9 could have done better in the German court case. At a minimum they could have asked users to register and provide proof of residency, and then could have ensured that their DNS service is offered only to registered users.
This would have been a massive burden to them, and (as we have seen from the ongoing data leaks) a gigantic privacy risk to its users. It would have also been a big overreach, as the German ruling would have mostly impacted non-German users.
If you can solve this for me it would actually help a lot at work :D
A recursive DNS resolver is identified just by an IP address for your system level DNS resolver to use (eg. in /etc/resolv.conf). Even if you assigned a random, secret IPv6 address for every individual user, they could simply share that with anyone else too. In IPv4, pretty much impossible.
Again, I don’t endorse that framing. But that’s where a lot of lawmakers are at. They’re not corrupt or fascists or hysterical about porn or whatever (well, plenty are, but not most). They’re trying to correct what they identify as a dangerously uncontrolled area.