Samsung really, really wants you to use Bixby. That's why it has included a physical button to access its woefully underpowered assistant on most phones since the Galaxy S8. Samsung has traditionally tried to prevent remapping that button, but the Galaxy S10 changed that. The official Bixby remapping feature from that phone is now spreading to Samsung's other devices.
So far, owners of both the Galaxy S9 and Galaxy S8 have seen the new Bixby functionality appear on their phones. It arrives via a Bixby update. So, if you put those off because you don't care about Bixby, now is the time to care a little bit.
Once you've got the latest update, the settings will include an option to tie Bixby to a single or double-press of the button. Whichever of those you don't have set for Bixby can launch another app of your choosing. So, you can push Bixby to a double-press and never use it while adding something useful to the single-press. This feature is part of Android Pie, so don't get too excited if your phone is still waiting for the OTA.