local and global state

components.child\.hbs

<div>
{{@name}} is open: {{if this.isOpen 'true' 'false'}}

<button {{on "click" this.open}}>open</button>
<button {{on "click" this.close}}>close</button>

</div>

components.child\.js

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';

export default class Child extends Component {
  #previousParentState;

  @tracked _isOpen;
  
  get isOpen() {
    if (this.args.isOpen !== this.#previousParentState) {
      this.#previousParentState = this.args.isOpen;
      this._isOpen = this.args.isOpen;
    }
    
    return this._isOpen;
  }

  @action open() {
    this._isOpen = true;
  }

  @action close() {
    this._isOpen = false;
  }
}

controllers.application\.js

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

export default class ApplicationController extends Controller {
  @tracked allOpen = false;

  @action toggleAll(state) {
    this.allOpen = state;
  }
}

templates.application\.hbs

<button {{on "click" (fn this.toggleAll true)}}>open all</button>
<button {{on "click" (fn this.toggleAll false)}}>close all</button>

<Child
  @name='child 1'
  @isOpen={{this.allOpen}}
/>

<Child
  @name='child 2'
  @isOpen={{this.allOpen}}
/>

<Child
  @name='child 3'
  @isOpen={{this.allOpen}}
/>

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"
  }
}