New Twiddle

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  
}

controllers.my-route\.js

import Controller from '@ember/controller';
import { tracked } from '@glimmer/tracking';

export default class MyRouteController extends Controller {
	queryParams = ['a'];
	@tracked a = null;
}

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('my-route');
});

export default Router;

routes.my-route\.js

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

export default class MyRoute extends Route{
	resetController(controller, isExiting) {
    if (isExiting) {
      // isExiting would be false if only the route's model was changing
      // controller.set('a', null);
      // controller.a = null;
    }
  }
}

templates.application\.hbs

<h1>Welcome</h1>

{{outlet}}

templates.index\.hbs

<div>
	<LinkTo @route="my-route">Go to My Route without a query params</LinkTo>
</div>

<div>
	<LinkTo @route="my-route" @query={{hash a="a1"}}>Go to My Route with a query param</LinkTo>
</div>

templates.my-route\.hbs

<LinkTo @route="index">Go Home</LinkTo>

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"
  }
}