Samsung will enable the Bixby Key Customization feature with an upcoming software update. You'll be able to open a specific app or run a quick command with a single or double press, and the other method will still activate Bixby.

While there have been workarounds to reassign the button, this is a straightforward, official way to make it more useful. If you're feeling cheeky, you might even remap it to open Google Assistant or Alexa if you prefer those to Samsung's own assistant.