Samsung is finally allowing us to disable the Bixby button, to an extent. The latest Bixby updates add a new toggle which lets you decide whether or not Bixby Home should be launched when the dedicated button is pressed. This can also be configured from the Bixby settings menu.
Even Samsung see the writing on the wall for their assistant at this point surely? Sadly their update only lets you make the button completely dead instead of letting you re-map it to something useful. There is of course a bunch of 3rd party software out there in Android land that allows you to do this.
Later Dixby.
Source: [Update] Samsung finally lets us disable the Bixby button – SamMobile