How to Solve
Exception java.lang.RuntimeException: Unable to start activity ComponentInfo{com.my.APP/com.my.APP.DownloaderActivity}: java.lang.IllegalArgumentException: com.my.APP: Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent.
Once I ran the app I received this error each time it crashed.
“Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent.
Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles.”

Solution: Update dependencies
Navigate to yourapp/android/build.gradle and add this line on dependencies.
if OneSignal Sdk is Implemented Then Upgrade it to latest version.
Add The Below Line In Your gradle And Run The App
implementation 'androidx.work:work-runtime:2.7.0-alpha01'
Also Important :
if You have Intent filters in your Manifiest Application activity
then You Must Add
android Exported ="true"