The Brief: Pop off is a phrase used to encourage someone.

DEEP DIVE
Stans use the phrase “pop off” to goad their icon on. It is used to show favor or support, especially in response to a large display of showmanship. It is a synonym for go off.
Notice how the best female dancers are all iconic 96 liners. oof queens pop off#Momo #Chungha #Seungyeon pic.twitter.com/YTaK7AKniM
— -Hobiuary- (@Tk_nayeon) January 31, 2019
ALRIGHT LATIN KING POP OFF pic.twitter.com/8OYoeycw0M
— mayra (@yoongisreina) February 6, 2019