Open Settings
Tap Advanced features
Tap Bixby key
Select Double press to open Bixby or Use single press for something else
Turn off Bixby key activation if the option is available
If needed, disable Bixby Home by turning off the Bixby Home toggle on the Home screen
If needed, remap the Bixby button to another app using a button remapper app
Restart the phone if the change does not take effect immediately