It is indeed complicated, I had a look at the source code of the Kando app and I believe I found what is required to make it work.
Could you check whether 6.208 works for you? (uploading now)
However the Kando app also seems to have issues with mouse-dragged events, the app's runloop seems to be blocked while the mouse is being dragged (which is expected if they don't specifically support mouse buttons, because this requires extra handling). Does this work for you?
It works fine with the trackpad for me
