ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Desktop.Core Namespace / Item Class / IsDefault Property

IsDefault Property (Item)
Gets if the item has been set as a default for this project
Syntax
public bool IsDefault {get;}
Remarks
For example, the project's home folder, default toolbox, and default geodatabase are default items.
Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

ArcGIS Pro version: 2.0 or higher.
See Also