Elasticsearch.Net NEST connection string when Active Directory turn on (Elasticsearch Authentication)

Elastic Stack Elasticsearch
7

Did you try using .BasicAuthentication() on ConnectionSettings?

By enabling Active Directory, have firewall settings on the machine been changed?

To rule out it being any issue with NEST, can you ping the cluster from the machine that is using NEST to connect to Elasticsearch, to see if the cluster can be reached. Use curl or PowerShell's Invoke-RestMethod for this.