Force a widget to rebuild from anywhere?

I cant really find a simple way to just rebuild a widget from outside it.

I guess this might be "by design", that you're not supposed to do it this way. But desperate times (deadlines) calls for desperate measures, so is there any way to tell a widget to rebuild (for example a Builder, or even the top most MaterialApp.builder) from anywhere in the code?

Note that I don't want to restart the application, just rebuild a specific widget somewhere in the widget tree.

Simplified example:

MaterialApp(
   
  builder: (context, child) {
    if( securityModel.appIsLocked ) then return LockScreen();
    return child;
  },

  home: MainScreen(),

  routes: {
    '/page1': (context) => Page1Screen(),
    '/page2': (context) => Page2Screen(),
  }

)


class SecurityModel(
  bool appIsLocked = false;

  void lockApp(){
    appIsLocked = true;

    /*******
     Force MaterialApp.builder() to rebuild, to replace the entire app with `LockScreen()` 
    *******/
  }
)
   

You could achieve this by wrapping your widget in a StreamBuilder widget. Then create a Stream on a global scope that you use as a parameter for your Streambuilder widget. You can then simply use the myGlobalStream.add(newValue) method from anywhere to update your widget. Let me know if you need a code sample, but it should be pretty straight-forward.