1. Использование пакета orientation:

   import 'package:orientation/orientation.dart';
   // Lock the screen orientation to portrait mode
   void lockOrientationPortrait() {
   Orientation.lockPortrait();
   }
   // Unlock the screen orientation
   void unlockOrientation() {
   Orientation.unlock();
   }
   // Lock the screen orientation to landscape mode
   void lockOrientationLandscape() {
   Orientation.lockLandscape();
   }
   // Lock the screen orientation to landscape mode, left only
   void lockOrientationLandscapeLeft() {
   Orientation.lockLandscapeLeft();
   }
   // Lock the screen orientation to landscape mode, right only
   void lockOrientationLandscapeRight() {
   Orientation.lockLandscapeRight();
   }

2. Использование класса SystemChrome:

   import 'package:flutter/services.dart';
   // Lock the screen orientation to portrait mode
   void lockOrientationPortrait() {
   SystemChrome.setPreferredOrientations([
   DeviceOrientation.portraitUp,
   DeviceOrientation.portraitDown,
   ]);
   }
   // Unlock the screen orientation
   void unlockOrientation() {
   SystemChrome.setPreferredOrientations([]);
   }
   // Lock the screen orientation to landscape mode
   void lockOrientationLandscape() {
   SystemChrome.setPreferredOrientations([
   DeviceOrientation.landscapeLeft,
   DeviceOrientation.landscapeRight,
   ]);
   }

3. Использование пакета screen:

   import 'package:screen/screen.dart';
   // Lock the screen orientation to portrait mode
   void lockOrientationPortrait() {
   Screen.keepOn(true);
   Screen.setOrientation(DeviceOrientation.portraitUp);
   }
   // Unlock the screen orientation
   void unlockOrientation() {
   Screen.keepOn(false);
   }
   // Lock the screen orientation to landscape mode
   void lockOrientationLandscape() {
   Screen.keepOn(true);
   Screen.setOrientation(DeviceOrientation.landscapeLeft);
   }

Обратите внимание, что в приведенных примерах кода предполагается, что вы уже импортировали необходимые пакеты в свой проект Flutter.