I experimented with a small stream deck unit.
As far as I could see it does not support sending or receiving midi. I used it to turn stops on and off by first assigning keyboard (computer keyboard) keys to operate the stops ( in Hauptwerk) and then used the stream deck software to assign the buttons to send the keyboard keys I had assigned to operate stops when the buttons were pressed. The unit did not light the buttons when the stops were operated by anything other than the stream deck buttons and so the illumination could be out of step with reality. There are API libraries if you wanted to write a midi to stream deck application. In my opinion, It was not a viable option for Hauptwerk without doing quite a bit of work.
Iain