jman0 wrote:

Just in case you didn't try or know (sorry if this sounds stupid) in order to launch the camera app with the button, you must long press it, not just a single short press. I'm saying this because when I got the phone I thought it didn't work because of that. I just tried on my phone (updated yesterday to 20180124 firmware) and it works.

Then, if you want to take a photo when the camera app is open, the button only works on stock camera.