dw-guten/metabox.php

<?php
/**
 * Register the post meta exposed in the block-editor "Post Meta" sidebar.
 *
 *   media               -> OpenGraph og:video URL   (emitted in theme inc/tweaks.php)
 *   featured_image_url  -> OpenGraph og:image URL    (fallback when no thumbnail)
 *   meta_desc           -> meta name="description"   (theme dw_meta_desc)
 *
 * show_in_rest is required so the values are editable from the block editor.
 */

defined( 'ABSPATH' ) || exit;

function dw_guten_register_meta() {
	$fields = array(
		'media'              => 'esc_url_raw',
		'featured_image_url' => 'esc_url_raw',
		'meta_desc'          => 'sanitize_textarea_field',
	);

	foreach ( $fields as $key => $sanitize ) {
		register_post_meta( 'post', $key, array(
			'show_in_rest'      => true,
			'single'            => true,
			'type'              => 'string',
			'sanitize_callback' => $sanitize,
			'auth_callback'     => function () {
				return current_user_can( 'edit_posts' );
			},
		) );
	}
}
add_action( 'init', 'dw_guten_register_meta' );