Just after installing any version of OpenCart you may notice that if you have multiple level categories in your store, subcategory products are not shown in parent or top category. That might be an issue for some. But there is a simple and quick solution for that. You just need vQmod in your system and one small free OpenCart extension.
How to show subcategory products on parent category pages – free OpenCart extension
Here is the free OpenCart extension you need – extension link. It officially shows that it supports OpenCart v1.5 versions, but it’s tested in latest versions including OpenCart v22.214.171.124 and it does it’s job perfectly. Extension shows products not only from the first level deep child categories, but from any level of categories.
For example you have categories:
Components >> Monitors
Components >> Printers >> Laser printers
By default Monitors won't show in Components category page. But with this extension OpenCart will show the child category products like monitors, printers, and even the products from their child categories.
Unfortunately I could not find a free OCMOD extension which does the same thing. But there's a paid extension that does exactly the same thing -> Subcategory Products in Parent Category Page.