Vanilla Select in out-of-box Ember

controllers.application\.js

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

export default class ApplicationController extends Controller {
  @tracked selected = 2;

  get isSelected() {
    // The {{get}} helper will coerce values to strings. Thus
    // an POJO lookup works even if the type is a number.
    return { [this.selected]: true };
  }

  @action
  update({ target }) {
    // This is where you convert a string version of the data
    // to the type associated with the data. In this example
    // it is a number associated to the index of the options
    // array used in the {{#each}} block. It could easily be
    // a model ID. 
    this.selected = parseInt(target.value, 10);
  }
}

templates.application\.hbs

{{#let (array "One" "Two" "Three" "Four") as |options|}}

  <h1>Selected: {{get options this.selected}}</h1>

  <select {{on "change" this.update}}>
    {{#each options as |label index|}}
      {{! index is a number but assigning to an HTML attribute will coerce it to a string }}
      <option value={{index}} selected={{get this.isSelected index}}>{{label}}</option>
    {{/each}}
  </select>

{{/let}}

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"
  }
}