If you use Concurrent Use licensing for ArcGIS Pro or ArcMap, you will need to upgrade your ArcGIS License Manager to 2019.0 before upgrading to ArcGIS Pro 2.4 or ArcMap 10.7.1.
If you are using ArcGIS Enterprise to manage your ArcGIS Pro Named User license, you will need to upgrade your ArcGIS License Manager to 2019.0 before upgrading to ArcGIS Pro 2.4.
ArcGIS License Manager 2019.0 is backwards compatible with earlier versions of ArcGIS Pro and ArcMap.
Concurrent Use licensing enables multiple users to share access to ArcGIS Desktop applications (ArcGIS Pro and ArcMap) on a network. ArcGIS License Manager, installed on the network, manages access and use of the Concurrent Use licenses for the users of the network.
Learn how to upgrade ArcGIS License Manager.