Her derTöne的注释向您显示了新语法，但是您还需要在setCategory之后激活音频会话:

Her der Töne's comment shows you the new syntax, but you also need to activate the audio session after setCategory:

do {
    try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default)
    try AVAudioSession.sharedInstance().setActive(true)
} catch {
    print(error)
}