music from iTunes not on new iPhone after backup

AlexHMM20 wrote:

How to I transfer the music from my MacBook Pro to my new iPhone Xs Max?

you sync your music to your phone using itunes. Sync your iPhone, iPad, or iPod using iTunes on your computer - Apple Support

To add to razmee209's response, with which I agree, note you need iTunes 12.9 or later to communicate to your iOS 12 device from your Mac.