ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Desktop.Core Namespace / CustomItemBase Class / Fetch Method

Fetch Method
Overload List
OverloadDescription
Custom items that are containers should implement fetch to populate their child items when they are expanded for the first time in Catalog.  
Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

ArcGIS Pro version: 2.4 or higher.
See Also