This article explains how to close apps on iPhone 12. It also debunks the misconception that closing apps saves battery life.
Closing apps is also called quitting apps, forcing apps to close, or forcing apps to close.
To close apps on iPhone 12, follow these steps:
From any screen on iPhone 12 (the Home screen or within an app), swipe up from the bottom of the screen. You can swipe as far as you want, but about 25% of the way up is enough.