I’m demoing Cubase Elemennts 10 and purchased Cubase Pro 10.
I have the latest revision Macbook Pro 2018 and Apple changed the audio configuration so that when you plug in headphones it creates a new Sound device instead of internally routing the Speaker out to the headphones port.
This article from Rogue Amoeba describes it better than I can
But as this relates to Cubase, when I start cubase and have my headphones plugged in I have a choice of two Built-In Audio devices
The 2nd Built-In audio seems to be the headphone port but it’s always a guess. Hopefully that is an easy fix