quasar-config.ts: "Vue: Cannot find module #q-app/wrappers or its corresponding type declarations."

[nkamp]

I'm the whole day bussy to find out, and I'm looking at the quasar 'playground'.
I've inherited a project which started in 2018 I believe, so it is not the state of art...?

The main problem is I think, that quasar is not loaded. The HTML tags keep the quasar component sign like:
<q-header class="..."...>... instead of <header class="..." ...>.... And also not all the class definitions are added to the class attributes.

Now I want to upgrade Node.Js version 16 ==> version 22 and the dependencies including quasar 2.11.x to 2.18.6.
It is made with Vue 3.5.25, webpack 5.103.0. (not with Vite)

This is my quasar-conf.ts:

import { defineConfig } from "#q-app/wrappers";
// import "./styles/app.scss";
// import "@quasar/extras/mdi-v5/mdi-v5.css";
import iconSet from "quasar/icon-set/mdi-v5";
import langNl from "quasar/lang/nl";

export default defineConfig((/* ctx */) => {
  return {
    eslint: {
      warnings: true,
      errors: true,
    },
    boot: [],
    css: ["app.scss"],
    extras: ["mdi-v5"],
    build: {
      vueRouterMode: "history", // available values: 'hash', 'history'
    },
    config: {
      loadingBar: {
        position: "bottom",
        color: "primary",
        size: "6px",
        ref: "loadingBar",
      },
    },
    framework: {
      iconSet: "mdi-v5", // Quasar icon set
      lang: "nl-NL", // Quasar language pack

      config: {},

      // Quasar plugins
      plugins: ["...", "..."],
    },
    animations: [],
  };
});

I get an error for the
import { defineConfig } from "#q-app/wrappers";

In this project there is not a '.quasar' file. I read that I should add "extends": "./.quasar/tsconfig.json", , so I do not understand why I should add this.

In the main.ts there the quasar configuration should be loaded with

useConfig()
  .fetchConfig()
  .then(() => {
    const  = 
       ....
      .use(Quasar, quasarConf as any)
      .use(...
      ....
});

I can't find the q-app in the node_modules. I can find quasar/wrappers, but if I use that then the 'defineConfig' can't be found.

So what is missing or what do I not understand?