I don't recall it being there for the .5 camera, but I may have missed it. The current Microsoft description for photos (https://www.microsoft.com/en-us/d/surface-duo-2/9408kgxp4xjl?SilentAuth=1&wa=wsignin1.0&activetab=pivot:techspecstab) says "Portrait mode with adjustable depth control. Portrait mode supported for wide and tele camera. Machine learning used for portrait mode." Is this inconsistent with only the two options for Portrait mode?
I looked around for reviews, etc. that discussed this and all that discussed Portrait had the description that Microsoft has. One review on October 21, 2021 (https://mspoweruser.com/microsoft-surface-duo-triple-camera-snapdragon-888/) has the same description for Portrait mode listed as what Microsoft shows.
By the way in Photo mode I'm able to pinch with the .5 camera, and it transitions to the 1. camera when the zoom reaches that point, and then transitions to the next camera again when the zoom reaches 2x, and can be increased to 10x as expected. For Portrait mode there is no pinch.