WP-JSON OEMBED (TAG REL=) | WordPress.org

This is related to the oEmbed provider. I recommend using a plugin such as Disable Embeds if you don’t need or want oEmbed support.

Interesting! Thanks so much for the IMMEDIATE response!

For those who want to disable without using plugins:

function disable_wp_oembeds() {
  // Remove the REST API endpoint.
  remove_action('rest_api_init', 'wp_oembed_register_route');
  // Turn off oEmbed auto discovery.
  add_filter('embed_oembed_discover', '__return_false');
  // Don't filter oEmbed results.
  remove_filter('oembed_dataparse', 'wp_filter_oembed_result', 10);
  // Remove oEmbed discovery links.
  remove_action('wp_head', 'wp_oembed_add_discovery_links');
  // Remove oEmbed-specific JavaScript from the front-end and back-end.
  remove_action('wp_head', 'wp_oembed_add_host_js');
}
add_action('init', 'disable_wp_oembeds');