Southampton singer/songwriter Tom Mann made his first pop-music splash in the early 2010s, when he landed in the X Factor-conjured boy band Stereo Kicks. Since then, he’s brought his knowledge of pop music to a slew of other artists. His savvy helped make the Regard/Troye Sivan/Tate McRae collaboration “You” a sumptuous synth-pop jam, while his work with Lewis Capaldi and James TW showcases his sensitive side.