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:

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