It just happened on Samsung Keyboard, the Google Keyboard or Microsoft Keyboard Swiftkey is works fine.
Please see the video for more detail:
https://user-images.githubusercontent.com/22168484/115704505-a6deb580-a395-11eb-9209-2331e40cb601.mp4

Sample code:
TextFormField( decoration: const InputDecoration(icon: Icon(Icons.person), hintText: 'hint nè nè nè', labelText: 'Ngọc trung nè', ), keyboardType: TextInputType.emailAddress, ),

Here is flutter doctor -v:
`[√] Flutter (Channel stable, 2.0.5, on Microsoft Windows [Version 10.0.19042.928], locale en-US)
• Flutter version 2.0.5 at D:\2-Software\FlutterSDK
• Framework revision adc6878 (6 days ago), 2021-04-16 09:40:20 -0700
• Engine revision b09f014
• Dart version 2.12.3

[√] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
• Android SDK at D:\2-Software\AndroidSDK
• Platform android-30, build-tools 30.0.2
• ANDROID_HOME = D:\2-Software\AndroidSDK
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
• All Android licenses accepted.

[√] Chrome - develop for the web
• Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.1.0)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code (version 1.55.2)
• VS Code at C:\Users\trung\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 3.21.0

[√] Connected device (4 available)
• SM N980F (mobile) • RF8N80WSREL • android-arm64 • Android 11 (API 30)

• No issues found!`

P/s: Press and hold the backspace key, it's working fine.