Why is electron-forge vue2 renderer failing to load properly without a dummy HTML file?

I started migrating from Electron 10 to Electron 20 using electron-forge. It seems that I must include an index.html as the entry point, when in the past I only needed to provide a simple Vue loader in a typescript file. For example, this is what I need to make the current flow work:

index.html

<div id="app"></div>

index.ts

import createApp  from 'vue';
import App from './App.vue';
new createApp(App).$mount('#app');

App.vue

<template>
<h1>Foo</h1>
</template>
<script lang='ts'>
</script>
<style >
</style>

package.json

          "@electron-forge/plugin-webpack",
          {
            "mainConfig": "./webpack.main.config.js",
            "renderer": {
              "config": "./webpack.renderer.config.js",
              "entryPoints": [
                {
                  "html": "./src/renderer/index.html",
                  "js": "./src/renderer/index.ts",
                  "name": "main_window"
                }
              ]
            }
          }

Seems really excessive when this worked fine in the past with no dummy HTML file:

import Vue from 'vue';
import App from './App.vue';
new Vue({
  el: '#app',
  template: '<App />',
  components: { App }
});

However this just results in an error with this in the display:

/*
 * ATTENTION: An "eval-source-map" devtool has been used.
 * This devtool is neither made for production nor for readable output files.
 * It uses "eval()" calls to create a separate source file w
:

Very confusing.