You have two screens — the menu and the cart — but they don't live together. You need navigation: how to move from one to the other and back.

Android has Navigation 3 (Nav3) for this — a new approach. Old Navigation 2 kept a separate "graph"; Nav3's idea is simpler: the back stack is just a list of screens that you control.

backStack = [ Menu ]                 ← on launch
tap the cart:
backStack = [ Menu, Cart ]           ← Cart "on top"
press Back:
backStack = [ Menu ]                 ← Cart pops off, back to Menu

Three parts:

• Screen — each destination as a NavKey (Menu, Cart, MenuItemDetail(itemId)). Not UI — an "address".
• rememberNavBackStack(Screen.Menu) — creates the stack starting at the menu; it survives rotation.
• NavDisplay + entryProvider — maps each Screen to its composable and draws the top of the stack.

Navigating = pushing onto the stack (backStack.add(Screen.Cart)). Going back = the system pops the top when you press Back.

Worth knowing (verify the docs). Navigation 3 is still alpha — the API and imports (androidx.navigation3.runtime, androidx.navigation3.ui) shift between alpha releases. This course's code is written against 1.1.4; if your version is newer, some names may differ — check the official docs. The idea (screens as keys, the stack as a list) stays the same.

Let's build: first the screen "addresses", then the graph.