Apple Music
Why does Apple Music only work on WiFi?
iPhone 8, iOS 12
Apple Music works on cellular, on Wi-Fi, and you can download selected tracks for completely offline use.
If you want to allow apps to use cellular data, then there is a general settings for that (Settings﹥Cellular﹥Cellular Data﹥On|Off).
If you want Apple Music to work on cellular, then verify that the Music app on your device is set to allow cellular data use. Settings﹥Cellular﹥(scroll down) Cellular Data per App﹥Music﹥On|Off.