How does Google deal with Shell Apps?

We can get some information about how Google deals with shell apps here:

https://developers.google.com/web/fundamentals/architecture/app-shell

As developers they themselves like shell apps.

But what about search engine optimization (SEO)?

How do Google web crawlers index shell apps?

https://developers.google.com/search/docs/advanced/javascript/javascript-seo-basics

My main takeaway is that:

• Special configuration is required, and

• Google has a ‘headless’ version of the Chromium browser which can simulate a real user

  • Kind of amazing! Now I get why owning the browser market is so important to Google!

So in theory it can be done. But how can we be sure?