As long as they’re configured to support public connectivity, public meaning across the internet, yes.
I think I create an non-Render MySQL host using JawsDB, but how to connected to the Render hosting, maybe to use the connection string or ?
There is nothing special about connecting to a MySQL service not on Render. You supply the connection details to the instance, configure the Hostname, Port, Username, Password, Database Name, by whatever means, and if it’s valid, you’re connected.