The ArcGIS License Manager for your Licensing Portal must be upgraded to support this version of ArcGIS Pro

Error Message

Attempts to launch the software after upgrading to ArcGIS Pro version 2.9 fail, and return the following error:

Error:   
The ArcGIS License Manager for your Licensing Portal must be upgraded to support this version of ArcGIS Pro.

Cause

The version of ArcGIS License Manager installed on the Portal for ArcGIS machine is not compatible with ArcGIS Pro 2.9. For more information on version compatibility, refer to License Manager Guide: Supported software products.

Solution or Workaround

Upgrade the license manager on the Portal for ArcGIS machine to ArcGIS License Manager 2021.1. Refer to License Manager Guide: License manager installation and startup for steps and more information.