I am using Getx for my state management. So When I Change MaterialApp to GetMaterialApp, the fontFamily switched back to the default.
pubspec.yaml file
flutter:
  uses-material-design: true
  fonts:
    - family: Sen
      fonts:
        - asset: assets/fonts/Sen-Regular.ttf
          weight: 300
        - asset: assets/fonts/Sen-Bold.ttf
          weight: 700
and I have saved Sen.ttf files in the assets/fonts folder

main.dart
Widget build(BuildContext context) {
    return GetMaterialApp(
      theme: ThemeData(
        colorScheme: ColorScheme.fromSwatch().copyWith(
        primary: kPrimaryColor,
        secondary: kSecondaryColor,
       ),
      fontFamily: "Sen"
      )
      debugShowCheckedModeBanner: false,
      home: const MainScreen(),
    );
  }
If I switch back to MaterialApp font will work fine.
Any help will be appreciated, Thank You.
 
                        
Once this happened to me while working with some google fonts. I tried different methods, there is nothing wrong with GetMaterialApp()
Option 1:
flutter cleanto clear all data, then update all the packages, and thenflutter pub getOption 2: Initialy this is what I did. In the textTheme, add
TextStylefor different types of text (headline1,bodyText1,etc)Option 3: If nothing works, try
flutter upgrade