Does storing host and port data in an app makes the server vulnerable?

I recently started development and was wondering. Every frontend application needs a host address and service port to connect to the backend server and the databases. For example when you use fetch in React you cannot avoid addressing the server, which can lead traces for many important internal services exposed, which can be extracted from the source code.

Doesn't that leave the system (backend server) exposed and vulnerable ?? And what can be best practice to avoid such thing from happening ?