Importing AngularJS 1.6 into Angular-Universal Project - angularjs

Question

We have a hybrid Angular6 and AngularJS 1.6 project which we are currently migrating. In this process, we also want to introduce Server Side Rendering (SSR).
The problem is, that the SSR is running in a node environment, so running the SSR/prerendering gets the following error:
npm-run ts-node ./prerender.ts
[..]/node_modules/angular/index.js:2
**module.exports = angular;**
**ReferenceError: angular is not defined**
at Object.<anonymous> ([..]/node_modules/angular/index.js:2:18)
at Module._compile (module.js:652:30)
at Object.Module._extensions..js (module.js:663:10)
at Module.load (module.js:565:32)
at tryModuleLoad (module.js:505:12)
at Function.Module._load (module.js:497:3)
at Module.require (module.js:596:17)
at require (internal/module.js:11:18)
at Object.angular ([..]/dist/server/webpack:/external "angular":1:1)
at _webpack_require_
([..]/dist/server/webpack:/webpack/bootstrap:19:1)
import 'zone.js/dist/zone-node';
import 'reflect-metadata';
import {renderModuleFactory} from '#angular/platform-server';
import {writeFileSync} from 'fs';
const globalAny:any = global;
const Window = require('window');
let window = new Window();
globalAny.window = window;
globalAny.document = window.document;
const {AppServerModuleNgFactory} = require('./dist/server/main');
renderModuleFactory(AppServerModuleNgFactory, {
document: '<app-root></app-root>',
url: '/'
})
.then(html => {
console.log('Pre-rendering successful, saving prerender.html');
writeFileSync('./prerender.html', html);
})
.catch(error => {
console.error('Error occurred:', error);
});
The Project is based on the universal-starter repo: https://github.com/angular/universal-starter
Any suggestions what's going on here?