WoWInterface - New items Highlighted

Hello, I am new to this forum and I have registered, because I am looking for information about a modification that I am trying to make to the game, it is something very "simple", I will detail it.
In the example game WoW Classic or Wow ltk classic, when looting items or buying items, the new items will be highlighted. I have tried several ways to implement it in wow ltk the old client but I don't get it.
Thank you and excuse my English I use a translator since I only speak Spanish.

Code:

local frame = CreateFrame("Frame")



function frame:OnEvent(event, arg1)

    if event == "BAG_UPDATE" then

        for bag = 0, 4 do

            for slot = 1, GetContainerNumSlots(bag) do

                local itemLink = GetContainerItemLink(bag, slot)

                if itemLink then

                    local _, _, _, _, _, _, _, _, _, _, _, itemClassID, itemSubClassID = GetItemInfo(itemLink)

                    local isNewItem = C_NewItems.IsNewItem(bag, slot)

                    

                    if isNewItem then

                        local itemButton = _G["ContainerFrame" .. bag + 1 .. "Item" .. slot]

                        if itemButton then

                            itemButton.NewItemTexture:Show() -- Mostrar la textura de nuevo ítem

                        end

                    end

                end

            end

        end

    end

end



frame:RegisterEvent("BAG_UPDATE")

frame:SetScript("OnEvent", frame.OnEvent)