NSX-T 2.4 enhanced its management plane with the support of NSX-T Manager Cluster.
NSX-T Managers Cluster offer a built-in VIP for high-availability.
But the usage of an external load balancer offers the following benefits:
NSX-T supports load balancing service, and the same NSX-T platform can be configured to load balance its NSX-T Managers Cluster.
This document describes this configuration and is valid for NSX-T 2.4 and more recent releases (like NSX-T 2.5 and NSX-T 3.0).