minimally it works

controllers.application\.js

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

class TAD {
  @tracked state = [0];

  get isLoaded() {
    return this.state[0] === 1;
  }

  get isError() {
    return this.state[0] === 2;
  }

  get isLoading() {
    return this.state[0] === 0;
  }

  get value() {
    return this.isLoaded ? this.state[1] : null;
  }

  get error() {
    return this.isError ? this.state[1] : null;
  }

  constructor(promise) {
    promise.then(
      (value) => this.state = [1, value],
      (error) => this.state = [2, error],
    );
  }
}

export default class ApplicationController extends Controller {
  @tracked something;

  setTo = (thing) => {
    switch (thing) {
      case 'pending':
        this.something = new TAD(new Promise(() => {}));
        break;
      case 'resolveNull':
        this.something = new TAD(Promise.resolve(null));
        break;
      case 'resolve12':
        this.something = new TAD(Promise.resolve(12));
        break;
      case 'errorNull':
        this.something = new TAD(Promise.reject(null));
        break;
      case 'errorWat':
        this.something = new TAD(Promise.reject('wat'));
        break;
      default:
        throw 'missing/unhandled case';
    }
  }
}

/*
<button {{on "click" (fn this.setTo 'pending')}}>set to pending</button>
<button {{on "click" (fn this.setTo 'resolveNull')}}>set to loaded(null)</button>
<button {{on "click" (fn this.setTo 'resolve12')}}>set to loaded(12)</button>
<button {{on "click" (fn this.setTo 'errorNull')}}>set to error(null)</button>
<button {{on "click" (fn this.setTo 'errorWat')}}>set to error("wat")</button>
*/

helpers.and\.js

import { helper } from '@ember/component/helper';

export default helper(function and([a, b]/*, hash*/) {
  return a && b;
});

templates.application\.hbs

<button {{on "click" (fn this.setTo 'pending')}}>set to pending</button>
<button {{on "click" (fn this.setTo 'resolveNull')}}>set to loaded(null)</button>
<button {{on "click" (fn this.setTo 'resolve12')}}>set to loaded(12)</button>
<button {{on "click" (fn this.setTo 'errorNull')}}>set to error(null)</button>
<button {{on "click" (fn this.setTo 'errorWat')}}>set to error("wat")</button>

{{#if (and this.something.isLoaded this.something.value)}}
  <p style='color: green;'>loaded with {{this.something.value}}</p>
{{else if this.something.isLoaded}}
  <p style='color: green;'>loaded with <code>null</code></p>
{{else if (and this.something.isError this.something.error)}}
  <p style='color: red;'>rejected with {{this.something.error}}</p>
{{else if this.something.isError}}
  <p style='color: red;'>rejected with <code>null</code></p>
{{else if this.something.isLoading}}
  <p>loading...</p>
{{else}}
  <p>🤷🏻‍♂️</p>
{{/if}}

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"
  }
}