iOS and Android Jumpstart with existing Rails app

Hi, I'm considering Jumpstart for the mobile part, I already have an existing Rails application.

Is there anyone who integrated an existing app with them? How difficult was it and what it required to do?

I know there is a doc page with the steps, but I'm more interested in real examples for real apps.

The doc page outlines all the minimum steps to integrate. Your app already needs to be running Turbo and Stimulus.js can be a hefty project if you're not already. 

Then you'll need to design how your app works on mobile which is going to be slightly different than mobile responsive in the browser since navigation will be native in iOS and Android.