Getting error "Cannot preview in this file"

Hello, I'm new to SwiftUI and right now I'm trying to create one simple Application by using @State, @ObservedObject, and @Environment.
For some reason, I got error "Cannot preview in this file" after I tried to add Environment object. The canvas is not working, but I can actually run the application in a simulator and actual device without any problem. Here is how I added my environment object.
SceneDelegate:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
        // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
        // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).

        let channelData = ChannelData()
        
        // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView().environmentObject(channelData)

        // Use a UIHostingController as window root view controller.
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible(



        }
    }

ChannelData class:

import Combine

final class ChannelData: ObservableObject{
    @Published var channelName = "YouTube Channel"
}

ContentView:

import SwiftUI

struct ContentView: View {
    
    @State private var showingSecondVC = false
    
    @ObservedObject var videoIdea = VideoIdea()
    
    @EnvironmentObject var channelData: ChannelData
    
    var body: some View {
        NavigationView{
            VStack(alignment: .leading){
                Text(videoIdea.title)
                    .font(.title)
                Text(videoIdea.contentIdea)
                    .font(.subheadline)
                Divider()
                NavigationLink(destination: ChannelView()){
                    Text("Add Channel")
                }
                Button(action: {
                    self.showingSecondVC.toggle()
                }){
                    Text("Add New Idea")
                }.sheet(isPresented: $showingSecondVC){
                    SecondView(videoTitle: self.$videoIdea.title, videoContent: self.$videoIdea.contentIdea).environmentObject(self.channelData)
                }
                Spacer()
            }.padding()
                
                .navigationBarTitle(channelData.channelName)
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

SecondView:

import SwiftUI

struct SecondView: View {
    
    @Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
    
    @Binding var videoTitle: String
    @Binding var videoContent: String
    
    @EnvironmentObject var channelData:ChannelData
    
    var body: some View {
        NavigationView {
            VStack(alignment: .leading){
                TextField("Video title", text: $videoTitle)
                TextField("Video Content", text: $videoContent)
                Divider()
                Button(action: {
                    self.presentationMode.wrappedValue.dismiss()
                }){
                    Text("Dismiss this VC")
                }
                Spacer()
            }.padding()
            
                .navigationBarTitle(channelData.channelName)
        }
    }
}

ChannelView:

import SwiftUI

struct ChannelView: View {
    @Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
    
    @State private var channelName = "My Channel"
    
    @EnvironmentObject var channelData: ChannelData
    
    var body: some View {
        NavigationView{
            VStack(alignment: .leading){
                TextField("Channel Name", text: $channelName)
                Divider()
                Button(action: {
                    self.presentationMode.wrappedValue.dismiss()
                }){
                    Text("Dismiss this VS")
                }
                Spacer()
            }.padding()
                .navigationBarTitle(channelData.channelName)
        }
    }
}