I'm still on Pie beta but bxActions isn't great. I've set Bixby to single press. It is impossible to disable Bixby. I have the button mapped to single press = back, long press = flashlight. Long press always launches flashlight and occasionally launches Bixby. Single press occasionally goes back and/or launches Bixby. It's too intermittent for me to really use back, but it's reliable enough for the flashlight. It's a shame really as I used to use it for back constantly! However, having the swipe gesture for back on the new navigation bar (which is totally hidden if enabled) means I don't miss it too much.