I found another helpful post from 2019 that used the direct entry to allow Compass to connect to the cluster for M121. It uses the same information so why does Compass connection string fail? When trying to connect with the below string it fails with a message connection closed.
mongodb://cluster0-shard-00-00-jxeqq.mongodb.net:27017,cluster0-shard-00-01-jxeqq.mongodb.net:27017,cluster0-shard-00-02-jxeqq.mongodb.net:27017/aggregations?replicaSet=Cluster0-shard-0 --authenticationDatabase admin --ssl -u m121 -p aggregations --norc
I can use the same string with mongo command and it works with terminal. The outgoing port tester shows the 27017 port open and while Compass wasn’t listed in the Firewall (Windows 10) I added it to be sure. Previous connection strings have worked with other courses. I pos ted this because there is an issue with the connection string in the course that should be resolved.