Test

controllers.application\.js

import Controller from '@ember/controller';
import { action, computed } from '@ember/object';
import { tracked } from '@glimmer/tracking';

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

  @tracked x = 0;
  @tracked y = 0;
  @tracked z = 0;
  untracked = 0;
  untrackedZ = 0;

  noGet() {
    console.log("noGet called")
    return this.x + this.y;
  }

  get propertyWithGet() {
    console.log("propertyWithGet called")
    return this.x + this.y;
  }

	@computed('x')
  get getWithComputedX() {
    console.log("getWithComputedX called")
    return this.x + this.y;
  }

	@computed('x','y')
  get getWithComputedXY() {
    console.log("getWithComputedXY called")
    return this.x + this.y;
  }

  @action incrementX() {
    this.x += 1;
  }
  @action incrementY() {
    this.y += 1;
  }
  @action incrementZ() {
    this.z += 1;
  }
  @action incrementUntracked() {
    // this.untracked += 1; // This will throw an assertion error
    this.set("untracked", this.untracked + 1);
  }
  @action incrementUntrackedZ() {
    this.untrackedZ += 1; // This will throw an assertion error
    console.log("this.untrackedZ", this.untrackedZ);
  }
}

templates.application\.hbs

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

X: {{x}}<br/>
Y: {{y}}<br/>
Z: {{z}}<br/>
noGet: {{noGet}}<br/>
propertyWithGet: {{propertyWithGet}}<br/>
getWithComputedX: {{getWithComputedX}}<br/>
nextIndexWithComputedXY: {{nextIndexWithComputedXY}}<br/>


<button {{on "click" this.incrementX}}>+1 X</button>
<button {{on "click" this.incrementY}}>+1 Y</button>
<button {{on "click" this.incrementZ}}>+1 Z</button>

<hr/>

Untracked: {{untracked}}<br/>
<button {{on "click" this.incrementUntracked}}>+1 Untracked</button>
<button {{on "click" this.incrementUntrackedZ}}>+1 UntrackedZ</button>
<br>
<br>

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"
  }
}