Cannot find '' in scope

I tested a simplified version of your code with no problem:

• App declaration

import SwiftUI

@main
struct ForumApp: App {
    @StateObject var model = Model()
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(model)
        }
    }
}

• Model file

import SwiftUI
import Combine

class Model: ObservableObject {
    @Published var showDetails: Bool = false
}

• ContentView

import SwiftUI

struct ContentView: View {
    @EnvironmentObject var model: Model
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
        }
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            ContentView()
                .environment(\.sizeCategory, .accessibilityLarge)
            ContentView()
                .preferredColorScheme(.dark)
                .previewDevice("iPhone 13 mini")
        }
        .environmentObject(Model())
    }
}

Could you show your project content:

I also tested in a MacOS App (your screenshots say it is MacOS) ; it works OK:

Hi, Im currently applying the changes that you post it. Thanks in advance for it. I will attach a screenshot and if you have the time I can send you the Xcode file by email.