React Redux - Confusion on Using Functional Component with useDispatch vs Class Component and mapStateToProps

I am trying to have a user be able to click an item from a list of all possible items and have a modal open to display data about that item (including the current quantity they have) and buttons to increment/decrement that amount.

To my understanding since I am just showing data that is being passed in and then dispatching an action to update the store I should be using a functional component to display the data and useDispatch to call the store action.

Currently when I update the store I see the change in Redux debugging tools but the change is not reflected in the modal until I reopen it. While I have been looking for answers to this I see many similar questions but they all use Class Components and mapStateToProps (such as this post). I thought best practices was to use functional components unless needed. Am I wrong to think that if I am getting a value from the store in a functional component it should update on change?

Code Snippets

• Dialog

export default function ItemDialog({
    ...
    selectedItem,
}) {
    const dispatch = useDispatch()
    const inventory = useSelector(
        state => state.user.inventory
    )
    let userItem = inventory.find(
        userItem => userItem.name === selectedItem.name
    )

    const changeItemCount = (item, change) => {
        item.change = change
        dispatch({
            type: "USER_INVENTORY_UPDATED",
            payload: item
        })
    }

    const showQuantity = userItem => {
        return userItem.quantity > 0 ? `(${userItem.quantity})` : ""
    }
...

render(
    <p className="text-xl text-center font-semibold">
        {selectedItem.name}
    </p>
    <p className="text-center font-light">
        {showQuantity(userItem)}
    </p>

    ...
    <AddBoxIcon
        onClick={() => changeItemCount(selectedItem, 1)}
    />
)

• Store

const userReducer = (state = InitialUserState, action) => {
    let inventoryCopy = { ...state.inventory }

    switch (action.type) {
        case "USER_INVENTORY_UPDATED":
            let category = action.payload.category
            let updatedItemIndex = inventoryCopy[category].findIndex(
                item => item.name === action.payload.name.toUpperCase()
            )

            // If item is already there
            if (updatedItemIndex >= 0) {
                inventoryCopy[category][updatedItemIndex].quantity +=
                    action.payload.change
            } else {
                // If item needs to be added to inventory category
                let newItem = {
                    name: action.payload.name,
                    quantity: action.payload.change
                }
                inventoryCopy[category].push(newItem)
            }

            return {
                ...state,
                inventory: inventoryCopy
            }

            ...

            default:
            return state
    }
}