Pretty much any data transfer from the EU to another country with laws that don’t comply with the GDPR is illegal, so that wouldn’t surprise me.

Well, illegal without explicit consent. And even then, the user should be informed about what data is being collected, where it goes, and what’s being done with it.

A simple We collect analytics data, do you consent? is technically not enough as far as I know. At least it shouldn’t be enough to be legal.