How to bar "Add To List" function for public?

Just published a new list:
Make Money Online With 15 Powerful And
Profitable Steps In A Daily Work Routine

How do I prevent people from adding items to the list?? I am a pro member and this is
a premium list.

Just edit your list settings and under engagement tab, turn off “Allow users to add items”

Also when you customize the embed code, you can turn various elements on or off such as the item tabs:

I used that tab and it is in the “Off” position. Is that correct?

yes, that’s correct.

With this setting turned “off” and you are logged in as the owner of the list, you will still see the add to list button that allows you to add to your list. Other users won’t see the button though. To confirm that, just go to your list on listly or on your blog in a incognito window.