While fully closing apps on your iPhone can keep it running at peak efficiency since it frees up memory and stops background refreshing, it's most critical when dealing with unresponsive apps. If you have an issue with a certain app, you can just force-close it instead of rebooting.
Ever since iOS 7, force-closing apps on all iPhones has remained the same and has carried over into iOS 11. You just double-click the Home button and swipe up on the unresponsive app to force it to quit. But the new iPhone X doesn't have a Home button ... so how do you do it?
Force-closing apps on the iPhone X is still very intuitive, and with a little bit of practice, can be mastered faster than you can say "Qi." However, it has one more step than on other iPhones, though, in iOS 12, force-closing apps on the iPhone X goes back to matching other iPhone models.
To access the app switcher, you'll need swipe up from the bottom of the screen, then pause with you finger in the middle of the screen for a second until all of the app cards appear. That pause is key. If you swipe too fast and don't hold, you'll just go back to the home screen.
- More Info: How to Use the App Switcher on the iPhone X
Unfortunately, it appears that you can no longer simply swipe apps away from the multitasking screen on the iPhone X to dismiss them — at least, not directly. When you swipe up on a card in the multitasking view, the phone interprets this as a Home button gesture and simply minimizes the app, taking you back to the home screen. When you swipe down on a card, the app goes into full screen.
So far, the only way we've found to properly close apps from the multitasking screen on the iPhone X is to use the older long-press gesture employed in iOS 4 through iOS 6. To try it out, just long-press any app in the multitasking UI, and a red button marked with a minus ( - ) sign will appear at the top of each card. From here, just tap the minus button to close any app of your choosing.
But the swipe-to-dismiss gesture isn't completely gone. When the red minus buttons are displayed, you can then swipe up on cards to force-close them. So you still can swipe up to close, but only with those red minus buttons present. If they aren't present, you will just be going back to the home screen.
With the iPhone X's interface being so gesture-based thanks to the bezel-less design and the lack of a home button, it's understandable that Apple has added an extra step to the swipe-up-to-dismiss gesture in the multitasking interface. After all, it wouldn't be very user-friendly if the same basic gesture performed different functions in different parts of the operating system.
Still, if you long for the days of old, be patient, because iOS 12 removed the press-and-hold step when force-closing apps which makes it match all other iPhone models.