[Galaxy S8/S8+] How to use the bixby button for other function?

Bixby key/button is a dedicate button to activate only Bixby service and to use
the key for other functions/applications is not supported.

With latest version of Bixby, you can set the button to do no action.

To turn off the Bixby Feature when pressing the Bixby Button, open Bixby, tap More option -> Settings -> Bixby Key.

Select "Don't open anything", Note that only the Bixby app won't open.

If you long press it, the Bixby voice will still activate.