why i should add the NoesisGUIPanel in the maincamera? for example i have alot of xaml files and i want them to be placed in separate objects in the scene not only the maincamera

You could place NoesisGUIPanel at any camera in the game. Just set properly order of rendering for it.
But most games uses NoesisGUIPanel in the main camera or in a single "overlay" camera which is used only for UI.

Modular UI doesn't mean you should break it into multiple cameras - you could use only single camera for it and dynamically add/remove objects from it's NoesisGUIPanel root object (usually Noesis.Grid used as root).
This way you also have some benefits like shared Logical/Visual Tree (so an UI element could access other elements in this tree) and performance/memory efficiency also: each NoesisGUIPanel instance has some overhead (offscreen buffer, etc).

You could place NoesisGUIPanel at any camera in the game. Just set properly order of rendering for it.
But most games uses NoesisGUIPanel in the main camera or in a single "overlay" camera which is used only for UI.

Modular UI doesn't mean you should break it into multiple cameras - you could use only single camera for it and dynamically add/remove objects from it's NoesisGUIPanel root object (usually Noesis.Grid used as root).
This way you also have some benefits like shared Logical/Visual Tree (so an UI element could access other elements in this tree) and performance/memory efficiency also: each NoesisGUIPanel instance has some overhead (offscreen buffer, etc).

sorry if i'm being stupid i'm new to NoesisGUI is there any way to change the current XAML of NoesisGUI?

The recommended approach is described here:

Best approach to switch/navigate between views

Basically, you have a root container in the NoesisGUI panel and dynamically add/remove XAMLs.

I also recommend you having a look at the MenuDemo sample

The recommended approach is described here:

Best approach to switch/navigate between views

Basically, you have a root container in the NoesisGUI panel and dynamically add/remove XAMLs.

I also recommend you having a look at the MenuDemo sample

great thanks i'm new to Xaml too