Routes in Jumbo follows the same structure React Router 6 offers to pass as an array to useRoutes hook (check this reference). However, there is one slight addition to this is the support of Middleware functionality.
You can find all the routes defined in for Jumbo inside the src/app/routes/ folder. Here, consider index.js as the file which combines all the other routes managed as per modules by merging the array and exporting the final routes array from here as default export.
To understand how Middleware functionality works, read Route Middleware topic here.