The sentence in question is perfectly grammatical. It follows the following pattern:

X is applicable whether a comparison is true (you have a closer connection to a foreign country than the United States during 2018).

This said, there's no relation between whether and than.

The sentence in question is perfectly grammatical, but as pointed out in Hot Licks' comment, it is poorly constructed -- almost designed to confuse. It follows the following pattern:

X is applicable whether a comparison is true (you have a closer connection to a foreign country than the United States during 2018).

This said, there's no relation between whether and than.