Incorrect (no keyboard support):

// app/components/dropdown.gjs
<template>
  <div class="dropdown" {{on "click" this.toggleMenu}}>
    Menu
    {{#if this.isOpen}}
      <div class="dropdown-menu">
        <div {{on "click" this.selectOption}}>Option 1</div>
        <div {{on "click" this.selectOption}}>Option 2</div>
      </div>
    {{/if}}
  </div>
</template>