What does this mean "a hot-button issue"?
I think it's an expression from USA.

Question

Answer

https://dictionary.cambridge.org/dictionary/english/hot-button#targetText=a%20subject%20that%20is%20important,something%20of%20a%20hot%20button.

hot button
noun [ C ] US informal
UK  /ˈhɒt ˌbʌt.ən/ US  /ˈhɑːt ˌbʌt̬.ən/
 
a subject that is important to people and about which they have strong opinions:

Answer

it means something that everyone is talking about at a given time - most time it is controversial