I'm in Germany, so definitely inside the EU. Though I'm using a non-European DNS (NextDNS) so maybe that has something to do with it?

The web site you are accessing doesn't get to know which DNS server you are using.

yes, and no. Some sites use DNS to route traffic to different servers for different regions. For instance you could have you site hosted on 2 different data-centers. 1 in EU and 1 in US. And then make US-centric DNS route traffic for your site to the US-datacenter and he EU-centric-dns to EU-data-center.

In that way you kinda know which DNS they used.

Yeah, it likely isn't using eDNS.

I'm glad I'm not the only one who couldn't figure out how to decline consent. I gave up; now, when I see "guce" at the beginning of the hostname, I bail.

Is there a form somewhere that can be used to report websites that do not comply with GDPR?

GDPR is a regulation enforced on a per country basis. The EU wrote it and the EU guarantees / enforces that all member states enforce it.

Therefore, talk to your local DPA. For example, in The Netherlands, you'd talk to the "Autoriteit Persoonsgegevens" (translated: Personal data protection agency"). All EU countries have some sort of governmental institution, usually named something along the lines of 'data protection agency'. As per the article, the one in Ireland is called "Irish Data Protection Commission (DPC)" – and they took the lead on blocking FB Dating.

If you're in the UK you can report it to the ICO (Information Commissioner's Office): https://ico.org.uk/make-a-complaint/.

They have a form specifically for reporting concerns with websites' use of cookies, see https://ico.org.uk/make-a-complaint/cookies/.