Show only one Subcategory in a Module not possible

Hi,

Categories listing modules display listings of categories (yes!).
So if you select a category, the system will display all the sub categories of that category.
If you don't have any category in it, it won't display anything.

So that's totally normal. There is no module to display the information of only one category.
The best you can do is to use such modules:
extensions.joomla.org/extensions/core-en...stom-code-in-modules
in order to manually add the text of your category with a link to it in a module.