Armament Haki got its upgrade in Wano, thanks to Hyogoro in Udon Prison. Luffy learned Ryuo, a trick to flow Haki out of his body and wreck stuff from the inside. He practiced on trees and collars ...

Luffy was able to manifest the advanced versions of Armament Haki and Conqueror's Haki. For the former, Luffy trained in the Prisoner Mine, and learned how to deal internal damage using Ryuo.