They can still do it to non-Europeans

How can they tell how an email address is European?

Because you told them while you were creating your Meta account, and because the credit card you entered matched what you told them.

Sure, but we are talking about shadow accounts, not Meta accounts.

Cost of doing business? Is GDPR protecting me as an American from Facebook shadow profiling me? How significant are GDPR fines?

In theory 4% from yearly revenue (not earnings, revenue), in practice I haven’t seen it being applied.

Here you go. Click your country's flag to see your results https://www.enforcementtracker.com (if you're European, that is).