Hey there,
I am really sorry for the delay of this reply as it is a weekend for us here.
You can not to show the module on certain page by setting the 'Module Assignment' to 'Only on the pages selected' or 'On all pages except those selected' from the 'Menu Assignment' tab of the module as shown in the screenshot for example. https://take.ms/Ql8ht
Also, I am really sorry that I miss out one point that you need to create
(Categories) Single Category menu item for each of your categories first so that you choose
'Only on the pages selected' then just uncheck the categories menu item that you don't want the showcase module to show up on it as shown in the screenshot from the quote for an example.
Can you try again and see how it goes?