CUBASE 9.5.1 not using kernels/processor power.

We use:

Imac Pro (2018)
CUBASE 9.5.1

When we process audio files (timestretching) it takes quite some time and according to activity monitor, Cubase doesn’t even use 1 of the 16 kernels available…

Also when exporting Audio the kernels are not utilised.

Is this a setting (or maybe IMAC PRO) or will it be fixed with a future update??

I appreciate your input regarding IMAC pro. My machine is acting differently and I wanted to see if yours does the same. When I hook a headphone to the computer, under the system pref and sound, the internal speakers are still active and showing. This is confusing Cubase .
Apple was not helpful. would you hook a headphone into yours and let me know how yours hehave?