When the British singer Arlo Parks released her first album, “Collapsed in Sunbeams,” in 2021, she appeared as a fully formed artist dealing in a soulful, musing alt-pop sound, her confessional songcraft glowing with all the wonder and angst of youth; it scored her the Mercury Prize, for the best record released in the U.K. or Ireland. Parks’s second album, “My Soft Machine,” released last year, felt a bit less personal but more ambitious by an order of magnitude, adding the producer Ariel Rechtshaid (Adele, Vampire Weekend) and the Brockhampton beat-maker Romil Hemnani to fill out its soft-rock palette. In the cradle-song melodies of a Phoebe Bridgers collaboration, “Pegasus,” and the SZA-ish dream-pop of “Puppy,” the hazy details of a reverie come into focus.—Sheldon Pearce