WordPress + ACF - Register fields via PHP

acf-page.php

<?php 
add_action( 'acf/init', 'register_allpage_fields' );
function register_allpage_fields() {
  $slug = "allpage";

  $fields = [
    [
      'key'       => 'page_subtitle',
      'label'     => 'Subtitle',
      'name'      => 'page_subtitle',
      'type'      => 'text',
    ],
  ];
  
  acf_add_local_field_group([
    'key' => "group_$slug",
    'title' => 'Options',
    'position'=> 'acf_after_title',
    'label_placement'   => 'left',
    'fields' => $fields,
    'location' => [
      [
        [
          'param' => 'post_type',
          'operator' => '==',
          'value' => "page",
        ]
      ]
    ]
  ]);
}
?>

functions.php

<?php 
/**
 * Import Custom Fields
 *
 * @see Import any custom acf fields in `includes/custom-fields` folder
 * @warning Required ACF Pro to be installed!
 */
foreach (glob(get_template_directory() . '/includes/custom-fields/*.php') as $file) {
  $filename = basename($file);
  require_once locate_template('/includes/custom-fields/' . $filename);
}

?>