Mac: Unable to switch between speaker and headphone outputs

When using Cubase (or other Steinberg ASIO hosts) with one of the latest Mac models, it is not possible to switch between the built-in speaker and the headphones on the fly by simply connecting a headphone. In the host, "two" "Built-in audio" options are available instead of the previous one.

The latest Mac models (from 2018) contain a built-in audio sub-system that is different from prior Intel HDA (High Definition Audio) architecture in Macs. Built-in audio functions are handled by a new component, so that the built-in audio hardware is now 'looking different' to audio apps running on the system. Among other things, it provides an independent built-in speaker and headphone output selection as a feature, which cannot be used correctly by our ASIO hosts at the moment.

Until we come up with a permanent solution, we suggest to create an aggregate device in the Audio MIDI setup (Applications - Utilities). See this link for details.
The newly created Aggregate Device can then be selected in Cubase/Nuendo under Studio ▸ Studio Setup ▸ VST Audio System ▸ ASIO Driver.