EU will presumably stop you from doing business in the EU, if you break EU laws and ignore judgments. Companies don't want that. Grindr LLC, a US company with no EU corporate presence as far as I know, was fined 6.5 million for breaching GDPR by an Oslo Court, upheld in appeals. They paid that fine. If they didn't, they'd probably be kicked out of the app stores from Norway (if not from all of EU). Apple and Google do have an EU presence. Even if they didn't, they wouldn't start a war over 23andMe.
We generally don't need to worry about EU judgments against US companies being enforced, or vice versa. It doesn't get far enough that we need to think about how it's going to be enforced as a practical matter.