New Twiddle

controllers.test\.js

import Controller from '@ember/controller';

export default class TestController extends Controller {
  // Remove this, and derived starts working
  // model;
  
  get derived() {
    return "The model is " + this.model; 
  }
}

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('test', { path: '/:param' });
});

export default Router;

routes.test\.js

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

export default Route.extend({
  model({ param }) {
    return param; 
  }
});

templates.application\.hbs

<LinkTo @route="test" @model="1">Test with 1</LinkTo>
<LinkTo @route="test" @model="2">Test with 2</LinkTo>

<div>
	{{outlet}}
</div>

templates.test\.hbs

{{this.derived}}

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"
  }
}