Fix WP stripping tags in multisite

unfiltered_html_filter.php

<?php
// In WP multisite, WP strips out things like script tags and embeds from the
// editor for non-super-admins. This filter allows editors to use these tags.
add_filter('map_meta_cap', function ($caps, $cap, $user_id, $args) {
  if (
    $cap === 'unfiltered_html'
    && (user_can($user_id, 'editor') || user_can($user_id, 'administrator'))
  ) {
    $caps = ['unfiltered_html'];
  }
  return $caps;
}, 10, 4);