How can I customize the action of the app. Both android and ios without modifying the xml of both platforms. Just using the screen view.
What kind of customisation you are referring to? Refer complete ActionBar documentation, you can add Custom Title View / Custom Action View.
I mean this kind of customization only action bars flutterawesome.com/…
Those are various different designs, not all are ActionBars. You will have to design them, there are some samples in market place