Simple Grid Theme Menu Not Working

Hi everyone!

I’ve already renamed the menus as categories_menu and header_menu but whenever I click on a menu item (for example, Photos), the posts under that category doesn’t show up. I also tried renaming it to category_menu though I don’t know if there’s a difference between the two spellings when it comes to its functionality.

I’ve also double-checked that the posts are under the right categories but they still won’t show up.

The pages show up okay, it’s just the posts under specific categories.

Welp!