Make second view gray SwiftUI

I have 2 views. 1 main view and 1 alert view. The alert view will appear in the front of the main view. I want to lower the white color from the entire main view when this happens. Like a gray or light gray when the alert view is on front.

My main view:

    struct MainView: View {
        @State private var showAlert = false


         var body: some View {

            VStack{ //multiple views
               
                  }//here I tried background, opacity, blur, but nothing works
                              
            
            if showAlert{
                   
                  AlertView(showAlert: $showAlert)              

            }

      }
    }

My alert view:

   struct AlertView View{
         let screenSize = UIScreen.main.bounds

         @Binding private var showAlert = false

         var body: some View {

            VStack{ //multiple views
        }
       .frame(width: screenSize.width * 0.85, height: screenSize.height * 0.7)
     
     }

  }

I tried using blur, background, opacity, but they still keep the color white. I want the entire background main view to change color, to be a bit gray when the alert view is open.

If you only need to change the greyscale value of the background view (no colored tints), use .brightness

Example:

struct MainView: View {
    @State private var showAlert = false


    var body: some View {

        VStack{
           // content
        }
        .brightness(showAlert ? -0.5 : 0)      //HERE
                              
            
        if showAlert {
              AlertView(showAlert: $showAlert)              
        }
   }
}

You could also try .overlay with a gray fill.

P.S. using this in combination with a small blur usually looks really good