ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Desktop.Mapping Namespace / Layer Class / Transparency Property

Transparency Property (Layer)
Gets the transparency value set to the layer. 100 being fully transparent and 0 means opaque.
Syntax
public double Transparency {get;}
Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

ArcGIS Pro version: 2.0 or higher.
See Also