Here’s how I made it work:
In the “Connect to host” page, leave the first section as is (localhost, 28017…) as we will be connecting from “inside” the droplev (via the SSH Tunnel). Only change the port if you also changed it in your DO Mongo.
Leave Authenthentication, Read Preference and SSL as they are, unless you have changed some of them inside your droplet. I believe these apply to the authentication of the databases, not your droplet.
Set up the SSH Tunnel with either:
3a. Use Password (that’s what I did): Use your droplet’s IP as the hostname, port 22, and your command line username and password, or
3b. Use an identity File (I’m assuming this is like the key file setup you might use in Putty)