SwiftUI: Change Binding's Value from Button's Action

Question

I have a cart item detail view with the "Add To Order" button. I want to increase the number of items (cartItem.count) when the button is tapped and wonder why this code doesn't update the UI (Text("(cartItem.count)")):

import SwiftUI

struct CartItemDetail: View {

@Binding var cartItem: CartItem

var body: some View {
    VStack {
        
        Text("\(cartItem.count)")
        Text(cartItem.product.name)
            .font(.largeTitle)
        cartItem.product.image
                        .resizable()
                        .frame(width: 200, height: 200).clipShape(Circle())
        
        Text("\(cartItem.product.price) | \(cartItem.product.calories)")
        Text(cartItem.product.description)
            .multilineTextAlignment(.center)
            .padding(.all, 20.0)
        Button(action: {
            cartItem.count = cartItem.count + 1
            })
        {
            RoundedButton(imageName: "cart.badge.plus", text: "Add to order")
        }
        
    }
}}

Some more code (if needed to reproduce)

struct ContentView: View {

@ObservedObject var cart: Cart

var body: some View {
    
    NavigationView {
        List($cart.cartItems) { $cartItem in
            
            NavigationLink(destination: CartItemDetail(cartItem: $cartItem)
                           
            ) {
                CartItemRow(cartItem:  $cartItem)
            }
        }
    }.navigationTitle("Cart")

}}

Cart and CartItem's code:

class Cart: ObservableObject {

@Published var cartItems: [CartItem]

init() {
    self.cartItems = []
    for product in testDataProducts {
        cartItems.append(CartItem(product: product, count: 1))
    }
}}

class CartItem: Identifiable {

var id: String
var product: Product
var count: Int

init(product: Product, count: Int) {
    self.id = UUID().uuidString
    self.product = product
    self.count = count
}}