Can I have two MaterialApp widgets in an app in Flutter

I have two questions with and "if" regarding the first question. As the title says I know it's better to have one MaterialApp in an App in Flutter and making Scaffold widgets for screens. But in a situation like this App which I followed for learning purposes and it's really written well and very clean. but it uses "TabBarView" as a default home for the entire app. So if I want to add another screen like "LoginSreen" that's not part of the "TabBarView" it's not inheriting the "MaterialApp" widget features. So I have to add a "MaterialApp" widget independently for that screen. So the question is, is it ok to have two "MaterialApp" widgets in a situation like this? if yes does it affect any variables that's shared among the screens like "SharedPreference"? or what does it affect? If it's a bad behavior to have two "MaterialApp" widgets to in an App, Then how can you get rid of the "NavScreen()" and implement the TabBarView in the screens, Because I have tried many ways and looked at many of open source projects like this they have "TabBarView" widget as the body and start of the project.