How do I run my app embed outside of Shopify Admin to test Web Vitals using Lighthouse

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Hello all,

I am trying to increase the performance of my app, it is embedded into Shopify admin using App bridge. To do this I need to run Lighthouse, however, Shopify mentions that Lighthouse might not work as the app embed is hosted inside of an iframe.

The Shopify admin uses an iFrame to display your app. Most local tools that measure Web Vitals metrics, such as Lighthouse, don’t accurately measure pages inside of iFrames. To use these tools to debug your app, run the app outside of the Shopify admin.
How do I actually run the app outside of the Shopify admin?
I am using the node-express template of an app.

I ran this command

cd web/frontend/ && SHOPIFY_API_KEY=REPLACE_ME npm run build

and then ran

cd web/frontend/ && npm run dev

But this is the error I get

vite v2.9.17 dev server running at:

  > Local:    http://localhost:3000/
  > Network:  http://192.168.1.3:3000/

  ready in 186ms.

1:45:19 PM [vite] http proxy error:
Error: connect ECONNREFUSED 127.0.0.1:80
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1602:16)

Can someone help me here, please