How is backend and frontend implemented as a single application?

Question

Node.js

Before that, I wrote in PHP + JS, but keeping 2 different servers for processing PHP and JS sides and, in principle, writing in two different languages ​​does not cause much joy. Especially after trying QuasarCLI.
If anyone has tutorials or even better video courses on creating a fullstack SPA application on NodeJS using Vue and MySQL, I would be very grateful.
At the moment I found the Nuxt framework ( nuxtjs.org ) but there is no example of the API from their demo mvc ( https://todomvc.nuxtjs.org ), but either I'm blind, or there really is no example of this API.
My biggest concern is MySQL data security. For many days I have been tormenting my head with how, for example, to hide server data. (no screenshot

spoiler

), because files and folders are visible there before they are rendered, and this is on a public host, not a local server. The source just shines for everyone.
Adepts of NodeJS/VueJS help with quality documentation and source codes for simple applications.

Answer 1

Before that I wrote in PHP + JS but keep 2 different servers for processing PHP and JS sides

I don't understand what you mean here...
full stack SPA ... you mean accessing the database and processing user data on the client? If so, then you really "tormented your head" ))
Start step by step, master the basics of Node.JS + Express. Work with data, queries in the database, data output from the database, and so on.
Master the template engine and only then start learning Vue.JS.
Once you understand the basic methods of working with Vue.JS, then implement the API on Node.JS.
The documentation on these technologies is excellent.
Maybe Node.JS seemed like a frontend to you? but this is not the case at all, but with the help of node.js + npm, you can build the frontend.
Maybe I didn’t understand you somewhere, until I read at the very “head is tormented”