> What's next, Meta has to prevent europeans who are currently in the US from accessing threads?

Here's what GDPR says it covers [1]:

1. In the case of processors or controllers established in the Union, all processing of personal data.

2. In the case of processors of controllers not established in the Union processing activities related to

2(A) the offering of goods or services to data subjects in the Union, or

2(B) monitoring to the behavior of data subjects as far as that behavior takes place in the Union.

If you are not in the Union and the entity processing your data is not established in the Union then GDPR does not apply.

[1] https://gdpr-info.eu/art-3-gdpr/