Forget all the stuff out there that says the GDPR protects EU citizens. This is a question of jurisdiction and enforcement. Say I run a blog under a business registered in the US funded by advertisers in the US. A EU citizen that comments on posts issues a GDPR request that I ignore. Their government fines me. I tell them to get bent, I am out of their jurisdiction. What can they do at that point?
This might help:
Law.stackedchange.com
Pretty much nothing if it’s digital services with no goods or payments in the EU.(unless the eu puts pressure on the 3rd countries government)