You can try to the way discussed here
To Hide the App :
PackageManager p = getPackageManager();
ComponentName componentName = new ComponentName(this,
com.apps.MainActivity.class); // activity which is first time open in
manifiest file which is declare as <category
android:name="android.intent.category.LAUNCHER" />p.setComponentEnabledSetting(componentName,PackageManager.COMPONENT_ENABLED_STA
TE_DISABLED, PackageManager.DONT_KILL_APP);
and to create a shortcut in dialer
<receiver android:name=".MySecretCodeReceiver">
<intent-filter>
<action android:name="android.provider.Telephony.SECRET_CODE" />
<data android:scheme="android_secret_code" android:host="1711" />
</intent-filter>
</receiver>
And since you are using flutter , it would be really hard to manage these methods as they are only possible to be used using java and are registered using the manifest.If you still want to make the app , i would suggest you to use java or kotlin in android studio and not flutter ,dart.