Binding DSE FN button?..

What is the easiest way to bind the FN buttons, on the DualSense Edge, to a keyboard button? I need one of them as the Z key for push-to-talk in BO6.

Steam Input? DSX? ReWASD?

I play BO6 on Bnet. If I used Steam Input (or any of them for that matter) would I need to leave the program running in the background?