SQL Doc not connecting to localhost or a publicly accessible RDS

I'm trialing SQL Doc and I can't get it to connect to a locally hosted MySQL database at localhost/127.0.0.1 or a publicly hosted AWS RDS instance.

I'm using the SQL Server Authentication option, I've tried localhost/loclahost:3306/127.0.0.1/127.0.0.1:3306 and entered my RDS endpoint. I have tried this connection settings with DBeaver and MySQL workbench and they connect just fine.

After pressing Connect, the loading animation spins for about 10 seconds and then I get this error:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that the SQL Server is configured to allow remote connections. (provider: named Pipes Provider, error 40 - Could not open a connection to SQL Server)