I want to switch to a new view when the login is successful And it will save the login state, when I close the App and open it again, no need to login again. I use combine . library .Hope you can help me. Thanks

Here is my full code. Hope you will help me

Firebase will tell you... you just need to ask. This is how you ask.

    let user = Auth.auth().currentUser
    if let user = user {
        // User is logged in
    }

These are the FirebaseAuth iOS docs (for further information)

Your should probably call this in the init of your LoginViewModel

    init() {
        let user = Auth.auth().currentUser
         if let user = user {
            // User is logged in
            session = User(uid: user.uid,
                           email: user.email)
        } else {
            session = nil
        }
     }

Make the LoginViewModel variable session @Published like this

    class LoginViewModel: ObservableObject {
        ...
        @Published var session: User?
        ...
    }

read about the Published type here

Update

You should add this block to your signIn() func in the LoginView in the else instead of session.isLoggedIn.toggle().

I also recommended removing the isLoggedin var you should look at the user object in session to check if it is nil or not.

    func signIn () {
        loading = true
        error = false
        session.signIn(email: email, password: password) { (result, error) in
            self.loading = false
            if error != nil {
                self.error = true
                self.loading = false
            } else {
                guard let uid = result?.user.uid,
                      let email = result?.user.email else {
                    return
                }
                session.session = User(uid: uid, email: email)
            }
        }
    }

This is the signUp() I added. Although I recommend making it on a separate page.

    func signUp (email: String,
                 password: String,
                 handler: @escaping AuthDataResultCallback) {
            Auth.auth().createUser(withEmail: email, password: password, completion: handler)
    }

Finally I would recommend to move all the login logic to the viewModel instead of the view... that's why viewModels exist.