What is API 31 in Android?
Audio focus. Starting with Android 12 (API level 31), when an app requests audio focus while another app has the focus and is playing, the system fades out the playing app. See Audio focus in Android 12 and higher for more details.
What is target SDK version?
android:targetSdkVersion — Specifies the API Level on which the application is designed to run. In some cases, this allows the application to use manifest elements or behaviors defined in the target API Level, rather than being restricted to using only those defined for the minimum API Level.