React update item quantity in the shopping cart

I'm trying to update the quantity of each item , i have tried my code but it didn't work correctly, but when i tried a solution found here: How to update item quantity in the shopping cart using React Redux , it worked thankfully . But i want to understand why my code didn't work (i'm using useContext not redux but normally that has nothing to do with the problem ) **Code that worked : ** :

cartItems: state.cartItems.map(item => item.id === payload.id
    ? {
      ...item,
      qty: item.qty + 1,
    }
    : item
  ),

**My unfunctional code : **

    if (productsInCard.find((x) => x.name === e.name)) {
  
    let qu ; //to get the new quantity
  const arr = [...productsInCard];
  productsInCard.forEach((ele, index) => {
    if (ele.name === e.name) {
      qu = ele.quantity + 1;
      console.log(ele.quantity + " this is the quantity before +1")

      arr.splice(index, 1);
      addCard(arr);
      console.log("old item deleted" + JSON.stringify(arr))

      addCard([
        ...productsInCard,
        {
          name: e.name,
          price: e.price,
          image: e.images[0],
          quantity: qu,
        },
      ]);
      addCard([
        ...productsInCard,
        {
          name: e.name,
          price: e.price,
          image: e.images[0],
          quantity: qu,
        },
      ]);
  console.log(" item + quantity added  : " +   JSON.stringify(productsInCard));

    }
  });
  
   const newArr = [...productsInCard] 
  productsInCard.forEach((ele, index)=>{

     if(ele.name === e.name){
      console.log(ele.quantity)
      if (ele.quantity < qu)
        newArr.splice(index, 1)
        addCard(newArr);
    } 
  }) 
} else {
  addCard([
    ...productsInCard,
    {
      name: e.name,
      price: e.price,
      image: e.images[0],
      quantity: 1,
    },
  ]);
  console.log("list with new item : " + productsInCard);
}

}