App upgrade listener proof of concept: https://blog.jakelee.co.uk/how-to-create-and-test-an-app-update-listener/

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          package="uk.co.jakelee.updatelistener">

    <application
            android:allowBackup="true"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>

        <receiver android:name=".AppUpgradeReceiver">
            <intent-filter>
                <action android:name="android.intent.action.MY_PACKAGE_REPLACED" />
            </intent-filter>
        </receiver>
    </application>

</manifest>

AppUpgradeReceiver.kt

class AppUpgradeReceiver : BroadcastReceiver() {

    @SuppressLint("UnsafeProtectedBroadcastReceiver")
    override fun onReceive(context: Context?, intent: Intent?) {
        if (context == null) {
            return
        }
        Toast.makeText(context, "Updated to version #${BuildConfig.VERSION_CODE}!", Toast.LENGTH_LONG).show()
    }

}