[Vecamia]

One issue I can see is that the guide you are using is from the old wowwiki archives.
Sadly, a lot on that website is outdated and no longer working.


I suggest instead to use https://wowpedia.fandom.com


Here is their more up to date guide on a dropdown menu:
https://wowpedia.fandom.com/wiki/Using_UIDropDownMenu


If you follow that guide, should be able to get a working version.


(the code from their guide)

local favoriteNumber = 42 -- A user-configurable setting
 
-- Create the dropdown, and configure its appearance
    local dropDown = CreateFrame("FRAME", "WPDemoDropDown", UIParent, "UIDropDownMenuTemplate")
    dropDown:SetPoint("CENTER")
    UIDropDownMenu_SetWidth(dropDown, 200)
    UIDropDownMenu_SetText(dropDown, "Favorite number: " .. favoriteNumber)
 
-- Create and bind the initialization function to the dropdown menu
    UIDropDownMenu_Initialize(dropDown, function(self, level, menuList)
    local info = UIDropDownMenu_CreateInfo()
        if (level or 1) == 1 then
        -- Display the 0-9, 10-19, ... groups
            for i=0,4 do
            info.text, info.checked = i*10 .. " - " .. (i*10+9), favoriteNumber >= i*10 and favoriteNumber <= (i*10+9)
            info.menuList, info.hasArrow = i, true
            UIDropDownMenu_AddButton(info)
            end
 
        else
        -- Display a nested group of 10 favorite number options
        info.func = self.SetValue
            for i=menuList*10, menuList*10+9 do
            info.text, info.arg1, info.checked = i, i, i == favoriteNumber
            UIDropDownMenu_AddButton(info, level)
            end
        end
end)
 
-- Implement the function to change the favoriteNumber
function dropDown:SetValue(newValue)
    favoriteNumber = newValue
    -- Update the text; if we merely wanted it to display newValue, we would not need to do this
    UIDropDownMenu_SetText(dropDown, "Favorite number: " .. favoriteNumber)
    -- Because this is called from a sub-menu, only that menu level is closed by default.
    -- Close the entire menu with this next call
    CloseDropDownMenus()
end