Deprecation Guide for Private property Route.router has been renamed to Route._router

The Route#router private API has been renamed to Route#_router to avoid collisions with user-defined properties or methods. If you want access to the router, you are probably better served injecting the router service into the route like this:

import Route from '@ember/routing/route';
import { inject as service } from '@ember/service';

export default Route.extend({
  router: service()
});