Luis J. González Maldonado is shaping the sound of Puerto Rico’s music scene. A partnership with fellow San Juan native Rauw Alejandro sent both to pop’s stratosphere in 2019, as Mr. Naisgai’s smooth blend of funk-tinged nostalgia coalesced into a cascade of platinum-selling singles. Serving as producer for a succession of stars, he transforms retro rhythms into post-genre dance-floor bangers.