Samsung is now offering the ability to remap the Bixby button on older flagships such as the Galaxy Note 9, S9/S9+, Note 8, and S8/S8+. The update is available via the Galaxy Store and allows the user to select a custom app to launch with either a single or double tap of the Bixby but not both. This means Bixby Home will continue to be available and the user cannot totally disable it.
https://www.notebookcheck.net/Bixby-remapping-now-available-on-older-Samsung-Galaxy-devices-as-well.411030.0.html