Demanding the ISPs to block traffic to Google domains would be quite effective.
Filter it based on what? Between ESNI and DNS over HTTPS, it shouldn’t be possible to know, which domain the traffic belongs to. Am I missing something?
Edit: Ah, I guess DNS over HTTPS isn’t enabled by default yet.
They probably also could just prevent EU companies and branches from buying google ads directly. Vast majority of ads is geo-located, so there would be almost no ads to show in the EU.