In most of Renders documentation, they mention that they handle SSL for you. This is only true when you are using their managed services like postgres or hosting.

When deploying MySQL, for example using render’s MySQL template, you wont get SSL out of the box. You’ll need to generate your own SSL certificates, add them to the mount volume for the service, and configure MySQL to both enable (and perhaps force) SSL and to use the certificates you’ve provided.

Once you’ve got MySQL up and running, you’ll need to give all the clients connecting to that database access to the public key to include as part of their connection requests.