sealed class ScreenAState() {
    object Loading : ScreenAState()
    object Ready : ScreenAState()
}

sealed class ScreenBState() {
    object Loading : ScreenAState()
    object Ready : ScreenAState()
}

sealed class Event {
    object DataSuccessfullyRetrieved : Event()
}

data class BackendDataObject(val stuff: Int)

class SharedViewModel {

    val screenAState = MutableStateFlow<ScreenAState>(ScreenAState.Loading)

    val screenBState = MutableStateFlow<ScreenAState>(ScreenAState.Loading)

    val events = MutableSharedFlow<Event>(
        extraBufferCapacity = 1,
        onBufferOverflow = BufferOverflow.DROP_OLDEST
    )

    // Some data that is set in Screen A, but retrieved in Screen B
    val someSharedObject = MutableStateFlow<BackendDataObject?>(null)

    fun submitThingFromScreenA(thing: String) {
        screenAState.value = ScreenAState.Loading
        backend.getDataObject(thing)
            .onSuccess {
                someSharedObject.value = it
                events.emit(Event.DataSuccessfullyRetrieved)
            }
    }
}

@Composable
fun ScreenA(viewModel: SharedViewModel, onNavigateToScreenB: () -> Unit) {

    LaunchedEffect(viewModel) {
        viewModel.events
            .onEach {
                onNavigateToScreenB()
            }
            .launchin(this)
    }

    Button(
        onClick = {
            viewMode.submitThingFromScreenA("thing")
        }
    )
}

@Composable
fun ScreenB(viewModel: SharedViewModel) {

    val sharedObject by viewModel.someSharedObject.collectAsState()
    
    ...
}

screenBState

screenBState

someSharedObject

BackendDataObject

BackendDataObject

BackendDataObject

class ScreenAViewModel {
    val screenAState = MutableStateFlow<ScreenAState>(ScreenAState.Loading)

    val events = MutableSharedFlow<Event>(
        extraBufferCapacity = 1,
        onBufferOverflow = BufferOverflow.DROP_OLDEST
    )

    fun submitThingFromScreenA(thing: String) {
        screenAState.value = ScreenAState.Loading
        backend.getDataObject(thing)
            .onSuccess {
                someSharedObject.value = it
                events.emit(Event.DataSuccessfullyRetrieved)
            }
    }
}

class ScreenBViewModel {

    val screenBState = MutableStateFlow<ScreenAState>(ScreenAState.Loading)
}

class SharedViewModel {

    // Some data that is set in Screen A, but retrieved in Screen B
    val someSharedObject = MutableStateFlow<BackendDataObject?>(null)
}

@Composable
fun ScreenA(screenAViewModel: ScreenAViewModel, sharedViewModel: SharedViewModel, onNavigateToScreenB: () -> Unit) {

    LaunchedEffect(screenAViewModel) {
        screenAViewModel.events
            .onEach { event ->
                when (event) {
                    is Event.DataSuccessfullyRetrieved -> {
                        sharedViewModel.someSharedObject = event.data
                        onNavigateToScreenB()
                    }
                }
            }
            .launchin(this)
    }

    Button(
        onClick = {
            screenAViewModel.submitThingFromScreenA("thing")
        }
    )
}