Removed size_hint_y: None and set explicit height and width using width: root.width * 0.8 and height: root.height * 0.6. Used FloatLayout for precise positioning. The pos_hint is used to ensure that the grid layout is centered both horizontally and vertically on the screen.

The new gridlayout section for scr 1 is below:

                GridLayout:
                    cols: 3
                    rows: 2
                    padding: "10dp"
                    spacing: "10dp"
                    size_hint: None, None  
                    width: root.width * 0.8  
                    height: root.height * 0.6  
                    pos_hint: {"center_x": 0.5, "center_y": 0.5}

Output:

Cheers!!!