WordPress: check if user is an adminstrator only by the wordpress_logged_in cookie (in case we need to do this check too early in the initialization of WP).

is_admin_user.php

function is_user_administrator(): bool {
    if ( function_exists( 'get_site_option' ) ) {
      $siteurl = get_site_option( 'siteurl' );

      if ( $siteurl ) {
        global $wpdb;
        $cookie_hash = 'wordpress_logged_in_' . md5( $siteurl );
        if ( ! isset( $_COOKIE[ $cookie_hash ] ) ) {
          return false;
        }
        $cookie = $_COOKIE[ $cookie_hash ];

        $cookie_parts = explode( '|', $cookie ); // 0 => user_login, 1 => expiration, 2 => token, 3 => hmac
        // check if the cookie has the correct number of parts
        if ( count( $cookie_parts ) !== 4 ) {
          return false;
        }

        $user_id = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->users WHERE user_login = %s", $cookie_parts[0] ) );
        if ( ! empty( $user_id ) ) {
          $capabilities = $wpdb->prefix . 'capabilities';
          $roles        = $wpdb->get_var( $wpdb->prepare( "SELECT meta_value FROM $wpdb->usermeta WHERE user_id = %d AND meta_key = '$capabilities'", $user_id ) );

          if ( empty( $roles ) ) {
            return false;
          }

          return strpos( $roles, 'administrator' ) !== false;
        }
      }
    }

    return false;
  }