1. a current, often controversial subject that people have strong opinions about
immigration has become a hot-button issue
If a button was really hot, you wouldn't want to touch it! In this figurative expression, a 'hot-button issue' is a subject or topic that a lot of people might avoid because it evokes anger or argument. Nowadays, issues like Climate Change, Transgender Rights, and Systemic Racism are 'hot-button issues' because people have very strong opinions about how to address them; and they regularly lead to heated arguments.