Runtime Error: Targeting S+ (version 31 and above) requires that one flag of FLAG_IMMUTABLE be specified[...]

[Anke]

See also here:

Change API version from aab file

I've no issues with your APK on one of my test devices (Galaxy Note8, Android 9). But maybe there are problems on Android 12+ [grafik] May @ewpatton enlighten us. https://developer.android.com/reference/android/app/PendingIntent