const oldProducts = [{ id: 1}, { id: 2}, { id: 3, smth: 2}, { id: 4}];
const products = [{ id: 3, smth: 5}, { id: 4}, { id: 5}, { id: 6}];

const oldUniq = oldProducts.filter(item => !products.some(elem => elem.id === item.id))

const updatedProducts = [...oldUniq, ...products];

console.log(updatedProducts);