What is the difference between TextFormField and TextField?

If you making a Form where you require save, reset, or validate
operations- use TextFormField. Else For Simple user input capture
TextField is sufficient.

TextFormField, which integrates with the Form widget.

This is a convenience widget that wraps a TextField widget in a FormField.

A Form ancestor is not required. The Form simply makes it easier to save, reset, or validate multiple fields at once.

To use without a Form, pass a GlobalKey to the constructor and use GlobalKey.currentState to save or reset the form field.

sample:

TextFormField(
  autovalidateMode: AutovalidateMode.always
  decoration: const InputDecoration(
    icon: Icon(Icons.person),
    hintText: 'What do people call you?',
    labelText: 'Name *',
  ),
  onSaved: (String value) {
    // This optional block of code can be used to run
    // code when the user saves the form.
  },
  validator: (String value) {
    return value.contains('@') ? 'Do not use the @ char.' : null;
  },
)

TextField, which is the underlying text field without the Form integration.

The text field calls the onChanged callback whenever the user changes the text in the field. If the user indicates that they are done typing in the field (e.g., by pressing a button on the soft keyboard), the text field calls the onSubmitted callback.