I had that problem with the x there is no home button so if you open the app notice toward the bottom of the screen a white line if you put your finger on it, it lights up just swipe up it should close the app.
That was copied and pasted right from the Apple support page for closing (shutting down) an app. I can only hope Apple knows how to accomplish the task, and publish it on their website. The method for previous models just prior to the section I copied was correct.
That is correct re closing apps completely on iphone x. But that is after the app is placed into the task switcher (swipe from bottom to right edge). Before that, swipe from bottom to center and hold for a moment to place an app in the switcher. However, as best as I can tell, the Breeze app does not respond to that gesture. The above post describes the white line and using that process places Breeze into the switcher and THEN your procedure completely closes the app.