In the Asset Explorer, objects are only displayed if their object type—or the object type of a parent object—has been enabled as the top-level node in the Asset Explorer. This article explains how to enable this.
Path to the starting point: Control Panel - Objects - Object Catalog - Object Types
Open the object type you want to activate
In the Asset Explorer section, select the "Display as top-level node" checkbox
Click Save in the toolbar
The objects of this object type and all child objects are now displayed in the Asset Explorer.