Getting error while creating a New Connection using Studio 3T for Mongo DB
As per MongoDB articles blog here The Connection Manager in Studio 3T makes it easy to connect to MongoDB, whether it is cloud-hosted or on-premise, or through a direct connection or a replica set.

Create a new connection


Open Studio 3T.
Click on the Connect button either in the global toolbar or under
the Recent Connections tab. This will open the Connection Manager.
Click on New Connection. This will open the New Connection window.



  Please note that with the release of Studio 3T 2018.6 and support for
  SCRAM-SHA-256, it will no longer be possible to connect to MongoDB
  version 2.6, which reached its end of life in October 2016. Only
  MongoDB versions 3.0 and higher are supported.


Studio 3T supports various settings nested under the Server, Authentication, SSL, SSH Tunnel, and Advanced tabs:

Server


Direct Connection
Replica Set or Sharded Cluster


Authentication


Basic (SCRAM-SHA-256)
Legacy (MongoDB-CR or SCRAM-SHA-1)
X.509
Kerberos (GSSAPI) - Enterprise only
LDAP (PLAIN) - Enterprise only


SSL


Accept any server SSL certificate
Use own Root CA file
Accept trusted server SSL certificates
Use Client Certificate
Allow invalid hostnames
User Server Name Indication


SSH Tunnel
 - Use SSH tunnel to connect

Advanced


Max. connection idle time
Server selection timeout
Socket timeout
Connect timeout


As I am able to see from attached screen shot as Studio 3T is showing the TRIAL License. Instead of Studio 3T IDE you can use the Robo 3T (formerly Robomongo) is the free lightweight GUI for MongoDB.

For example the simple new connection of Robo 3T (Robomongo) will be as follows:



For further your ref here , here and here