Unfortunately, HomeKit is not currently supported on macOS for native Mac apps like Portal. 

We’d absolutely love to support it and broaden the number of lights that Portal can support. So we’re hoping Apple decide to add native HomeKit support in the future.

NB. Confusingly, iOS apps running on Mac in compatibility mode and Mac Catalyst apps (iPad apps that can run on Mac) can use HomeKit. However, Portal for Mac is slightly different as it is a native Mac app. We built it this way to support features like motion desktop backgrounds and to be able to deliver a more integrated seamless experience.