Is there a definitive list of countries that use traditional chinese and those that use simplified chinese?
Hate to be pedantic, but Hongkong and Macau are not countries, but administrative regions within China. Furthermore, Taiwan’s status is a bit blurred because of the one China principle.

As for your question, Chinese is not official language in Malaysia, Philippines, and Indonesia, so the issue boils down to actual usage, which is mixed and differs by generations. Same with Chinese communities in the West, where the complex script is more common, though. Japan also uses a simplified script.

Only China (minus Hongkong and Macau) and Singapore use simplified officially.