I have this TextFormField in a Stateful widget
TextFormField(
decoration: InputDecoration(labelText: "Image URL"),
keyboardType: TextInputType.url,
textInputAction: TextInputAction.done,
)
The expected behavior is to see a checkmark button (instead of newline button) in my swiftkey keyboard on my Android device; but nothing has changed on the keyboard. I have tried another TextInputActions like Search and Send they appear properly.
Even flutter is a great platform, there are still some missing points need to be improved. So in your case most probably;
keyboardTypeis affecting the done button to not show up. So if you simply change yourkeyboardTypetoTextInputType.textyour keyboard will start showing checkmark icon.