Can you run the following command in a notebook using the same cluster you are using to connect:

%sh

nc -vz <hostname> <port>

This test will confirm us if we are able to communicate with the SQL server by using the port you are defining to connect. If the connection is not succeeded we might need to check if any firewall or security group is blocking the communication.

If it succeeds can you confirm you are using the latest jdbc driver version?