code: public static function start()
      {
          $compatibility = [
              self::SUBSITES => null,
          ];
  
          if (ClassInfo::exists(Subsite::class)) {
              $compatibility[self::SUBSITES] = Subsite::$disable_subsite_filter;
              Subsite::disable_subsite_filter(true);
          }
  
          return $compatibility;
      }
docs: Returns the state of other modules before compatibility mode is started.
  
  @return array