Parent Child model data lookup

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

controllers.parent.child\.js

import Controller from '@ember/controller';

export default Controller.extend({
  
  actions: { 
    setParent() {
      // set a property on the parent controller
      debugger;
      const controller = this.controllerFor('parent');
      debugger;
    }
  }
});

controllers.parent\.js

import Controller from '@ember/controller';

export default Controller.extend({
  enabled: false
  
});

router\.js

import EmberRouter from '@ember/routing/router';
import config from './config/environment';

const Router = EmberRouter.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('parent', function () {
    this.route('child')
  });
});

export default Router;

routes.parent.child\.js

import Route from '@ember/routing/route';

export default Route.extend({
  
  model() {
    const parent = this.modelFor('parent');
    parent.data = 'changed';
    
    return parent;
  },
});

routes.parent\.js

import Route from '@ember/routing/route';

export default Route.extend({
  model() {
    return {
      data: 'I am data that was fetched from the parent'
    }
  }
});

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.parent.child\.hbs

<br>
I am the child route<br>
{{model.data}}

<button {{action "setParent"}}> toggle</button>

templates.parent\.hbs

I am the parent route 
<br>
{{model.data}}

{{#if enabled}} 
<br>I am enabled
{{else}}
<br>I am not enabled
{{/if}}
{{outlet}}

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}