What does "act rules" mean here?
Native speaker’s answer
Rebecca
The words "act" and "rules" are two separate words here, and are not put together as a phrase. An "act" in this context refers to a performing group in a show. To "rule" here is an informal way of saying "does very good". So the full sentence here means that the group BTS did very well in the Hot 100 list because of their new song all in English.