如何将功能从使用WordPress medium_large更改为上传的原始文件？

I am currently trying to create a custom image size for WordPress. I am uploading my full size image (1,000px by 1,000px) using the Media Library, and trying to use the function's below in my functions.php file.

As you can see, I am trying to save another version that is exactly 50% of the original image's width and height. The function below is saving a new version, but it is using WordPress' medium_large (768px by 768px) image, which results in my image being saved at 384px by 384px instead of the desired 500px by 500px.

I tried changing WordPress' default medium_large size to 2000px by 2000px, but then the function below switched to using WordPress' thumbnail (150px by 150px) image, resulting in a 75px by 75px image.

How do I get the code below to use the original image, not one of WordPress' created image sizes (medium_large, thumbnail, etc)?

<?php
add_filter('wp_generate_attachment_metadata', 'half_size_attachment_meta', 10, 2);

function half_size_attachment_meta($metadata, $attachment_id) {
  foreach($metadata as $key => $value) {
    if (is_array($value)) {
      foreach($value as $image => $attr) {
        if (is_array($attr))
          half_size_create_images(get_attached_file($attachment_id), $attr['width'], $attr['height'], true);
      }
    }
  }
  return $metadata;
}

function half_size_create_images($file, $width, $height, $crop = false) {
  if ($width || $height) {
    $resized_file = wp_get_image_editor($file);
    if (!is_wp_error($resized_file)) {
      $filename = $resized_file - > generate_filename($width.
        'x'.$height.
        '-sml');

      $resized_file - > resize($width * 0.5, $height * 0.5, $crop);
      $resized_file - > save($filename);

      $info = $resized_file - > get_size();

      return array(
        'file' => wp_basename($filename),
        'width' => $info['width'],
        'height' => $info['height'],
      );
    }
  }
  return false;
}
?>

Edit: I am not looking to use add_image_size / the_post_thumbnail within the functions.php file. This doesn't force the creation of images, and doesn't allow for percentage based values.

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Create your new image size with builtin WP function add_image_size https://developer.wordpress.org/reference/functions/add_image_size/

then call it with the_post_thumbnail function https://developer.wordpress.org/reference/functions/the_post_thumbnail/