using the system back button from flutter driver

If you have adb installed on your machine, you can run a command to perform the backpress using a keyevent:

import 'dart:io';

await Process.run(
  'adb', 
  <String>['shell', 'input', 'keyevent', 'KEYCODE_BACK'], 
  runInShell: true,
);

Maybe this can help you

 await device.shellExec('input', <String>['keyevent', 'KEYCODE_BACK']);

Found in one of the official flutter driver tests link