Hi!
1. In the custom field filter the value which is assigned wit the two stars ** is going to be selected by default from the list. That is basically an “empty” selection, you can edit the text of that as you need it.
2. It is not showing because you don’t have any post tags created yet, see: https://i.imgur.com/Y4XLVjN.png
I guess the taxonomy something different for what you are looking for.
