If I want to use an uppercase keyboard in an OTPTextField widget in Flutter, I can use the textInputAction and textCapitalization properties to customize the keyboard behavior. Here's an example:

OTPTextField(
  length: 6,
  width: MediaQuery.of(context).size.width,
  fieldWidth: 50,
  style: TextStyle(fontSize: 20),
  textFieldAlignment: MainAxisAlignment.spaceAround,
  fieldStyle: FieldStyle.underline,
  onCompleted: (pin) {
    // Do something with the entered OTP.
  },
  textInputAction: TextInputAction.done,
  textCapitalization: TextCapitalization.characters,
),

In the above example, the textInputAction property is set to TextInputAction.done, which will display a "Done" button on the keyboard, and the textCapitalization property is set to TextCapitalization.characters, which will force the keyboard to display uppercase letters.