Just to make sure there is complete understanding, Enum and EnumList Dropdowns are not meant to add/edit data, merely to select data. They have enhanced so that you can ADD items when the item you seek is not present. But typically cannot edit an item from the dropdown.
Yes I am seeing the same thing you are - no field on the form when list is empty - but I believe it is by design. The ADD capability is for adding OTHER values and this only applies when you have manually added items to the list in the column definition. This feature is to be used when you have a list of common items you insert initially but want to accommodate other entries that are not common.
When you have NO items in this list then it makes sense not to show the Enum or EnumList column since their are no values to select from. Additionally, if no items then there is nothing to add OTHER values to.
In contrast, you could have a list of items show in an Enum or EnumList by placing a list selection expression in the Valid_If property of the column definition - e.g.
SELECT( Items[Item Name], true). When you add a list in this manner the “Allow other values” option does NOT apply.
In your case, a better fit might using a Ref column. To do this, create a separate utility table that is simply for listing the items, make your form entry column of Ref type and select the utility table as the source. When you reference the table in this way and it is empty, your dropdown will look like this: