In Glide Classic, there used to be 2 components to work with lists: inline list and list relation. Inline list displayed the entire list of items, list relation displayed a link to a screen with the list of items.
These two components were replaced by 1 component: collections.
On the details screen of the category, add an Action Row component (this visually resembles the list relation component), as the action select “Navigation / Show New Screen”, configure it to “This item” so the new screen is on the category/parent row, then add a collection whose data source is the relation category→item.