On my Samsung Galaxy S7 if I press two times the home button the camera will open. How can I disable this function? Where I've to go in settings?
I don't own a Galaxy S8 but I have the same feature on my Galaxy J5 that is called Quick Launch Camera.
To disable it, go to Settings > Advanced features > Quick Launch Camera and toggle it Off.
Additionally, there’s a Settings menu inside the camera app. Launch the camera and look for the gear-shaped settings button on the corner of the display. From here you can change the picture size, video quality, autofocus, ..., and the option for Quick launch camera. Toggle it On or Off.