I don't know what to put in the view placeholder

Question

I keep getting an error to insert "proxy: /GeometryProxy/" even when "proxy" is a state variable. I have the code for the preview below. I don't know what to put in the placeholder and I am confused. I have included my full code to review. Please look below.

struct MathematicallyMainController_Previews: PreviewProvider {
static var previews: some View {
    MathematicallyMainController(proxy: // what do i put here?)
}

}

My full code:

This is where the problem with the 'var' is happening.

struct MathematicallyMainController: View {
@StateObject var tabBarModel = TabBarViewModel()
@Environment(\.colorScheme) var colorScheme
@State var selectedIndex = 0
@State var isSelectedA = false
@State var isSelectedB = false
@State var isSelectedC = false
@State var isSelectedD = false
@State var isSelectedE = false
@State var proxy: GeometryProxy
var body: some View {
    ZStack {
        let bottomEdge = proxy.safeAreaInsets.bottom
        switch selectedIndex {
        case 0:
            HomeViewController()
        case 1:
            BrowseView()
        case 2:
            RewardsView()
        case 3:
            EssentialsView()
        case 4:
            SchoolModeView()
        default:
            HomeViewController()
        }
        ZStack {
            RoundedRectangle(cornerRadius: 15)
                .fill(.regularMaterial)
                .colorScheme(colorScheme == .dark ? .dark : .light)
            HStack(alignment: .center) {
                Button {
                   selectedIndex = 0
                } label: {
                    if selectedIndex == 0 {
                        ZStack {
                            Circle()
                                .blur(radius: 20)
                                .foregroundColor(.blue)
                                .frame(width: 60)
                                .padding([.leading, .trailing], 5)
                            Image(systemName: "house.fill")
                                .font(.title)
                                .foregroundColor(colorScheme == .dark ? .black : .white)
                                .padding([.leading, .trailing], 5)
                        }
                    } else {
                        Image(systemName: "house.fill")
                            .font(.title)
                            .foregroundColor(colorScheme == .dark ? .white : .black)
                    }
                }
                Button {
                    selectedIndex = 1
                } label: {
                    if selectedIndex == 1 {
                        ZStack {
                            Circle()
                                .blur(radius: 20)
                                .foregroundColor(.indigo)
                                .frame(width: 60)
                                .padding(.leading, 15)
                            Image(systemName: "rectangle.stack.fill")
                                .font(.title)
                                .foregroundColor(colorScheme == .dark ? .black : .white)
                                .padding(.leading, 15)
                        }
                    } else {
                        Image(systemName: "rectangle.stack.fill")
                            .font(.title)
                            .foregroundColor(colorScheme == .dark ? .white : .black)
                            .padding(.leading, 15)
                    }
                }
                Button {
                    selectedIndex = 2
                } label: {
                    if selectedIndex == 2 {
                        ZStack {
                            Circle()
                                .blur(radius: 20)
                                .foregroundColor(.orange)
                                .frame(width: 60)
                                .padding([.trailing, .leading], 15)
                            Image(systemName: "circle.dotted")
                                .font(.title)
                                .foregroundColor(colorScheme == .dark ? .black : .white)
                                .padding([.trailing, .leading], 15)
                        }
                    } else {
                        Image(systemName: "circle.dotted")
                            .font(.title)
                            .foregroundColor(colorScheme == .dark ? .white : .black)
                            .padding(.trailing, 15)
                            .padding(.leading, 15)
                    }
                }
                Button {
                    selectedIndex = 3
                } label: {
                    if selectedIndex == 3 {
                        ZStack {
                            Circle()
                                .blur(radius: 20)
                                .foregroundColor(.green)
                                .frame(width: 60)
                                .padding(.trailing, 15)
                            Image(systemName: "doc.text.image")
                                .font(.title)
                                .foregroundColor(colorScheme == .dark ? .black : .white)
                                .padding(.trailing, 15)
                        }
                    } else {
                        Image(systemName: "doc.text.image")
                            .font(.title)
                            .foregroundColor(colorScheme == .dark ? .white : .black)
                            .padding(.trailing, 15)
                    }
                }
                Button {
                    selectedIndex = 4
                } label: {
                    if selectedIndex == 4 {
                        ZStack {
                            Circle()
                                .blur(radius: 20)
                                .foregroundColor(.purple)
                                .frame(width: 60)
                                .padding([.leading, .trailing], 5)
                            Image(systemName: "graduationcap.fill")
                                .font(.title)
                                .foregroundColor(colorScheme == .dark ? .black : .white)
                                .padding([.leading, .trailing], 5)
                        }
                    } else {
                        Image(systemName: "graduationcap.fill")
                            .font(.title)
                            .foregroundColor(colorScheme == .dark ? .white : .black)
                    }
                }
            }
            .colorScheme(colorScheme == .dark ? .dark : .light)
            .padding(.horizontal)
        }
        .frame(height: 60)
        .shadow(color: .primary, radius: -10)
        .shadow(color: .black, radius: 10)
        .padding([.horizontal])
        .padding(.bottom)
        .frame(maxHeight: .infinity, alignment: .bottom)
        .modifier(OffsetModifier())
        .environmentObject(tabBarModel)
        .offset(y: tabBarModel.tabState == .floating ? 0 : bottomEdge)
    }
}

}

This is my ViewModifier I have included to create the scrolling animation.

struct OffsetModifier: ViewModifier {
@EnvironmentObject var model: TabBarViewModel
func body(content: Content) -> some View {
    content
        .overlay(
            GeometryReader { proxy -> Color in
                let minY = proxy.frame(in: .global).minY
                
                DispatchQueue.main.async {
                    
                    let durationOffset: CGFloat = 35
                    
                    if minY < model.offset {
                        if model.offset < 0 && -minY > (model.lastStoredOffset + durationOffset) {
                            withAnimation(.easeOut.speed(1)) {
                                model.tabState = .floating
                            }
                            model.lastStoredOffset = -model.offset
                        }
                    }
                    
                    if minY > model.offset && -minY < (model.lastStoredOffset + durationOffset) {
                        withAnimation(.easeOut.speed(1)) {
                            model.tabState = .expanded
                        }
                        model.lastStoredOffset = -model.offset
                    }
                    
                    model.offset = minY
                }
                return Color.clear
            }
            ,alignment: .top
        )
}

}