Apparently, if you enable “Compatibility Mode†for the bxActions application, which is available on the Play Store, you can turn the Bixby key into a shortcut to any action or application you want.
Unfortunately, we don’t have a Galaxy S8 locked to T-Mobile to give the bypass a try, but judging by the comments on Phandroid‘s post, it works like a charm.
Two-nil to the independent developers. It’s your move, Samsung.
Article source: https://www.technobuffalo.com/2017/07/13/bixby-button-remapping-is-working-on-the-galaxy-s8-again/