code: public function checkUpdate($currentVersion = null)
      {
          $lastVersion = $this->getLastVersion();
  
          if (!$lastVersion || version_compare($lastVersion, $currentVersion, '<=')) {
              return;
          }
  
          $versionPath = Config::XML_FASTLY_LAST_CHECKED_ISSUED_VERSION;
          $oldValue = $this->scopeConfig->getValue($versionPath);
  
          if (version_compare($oldValue, $lastVersion, '<')) {
              $this->configWriter->save($versionPath, $lastVersion);
  
              // save last version in db, and notify only if newly fetched last version is greater than stored version
              $inboxFactory = $this->_inboxFactory;
              $inbox = $inboxFactory->create();
              $inbox->addNotice(
                  'Fastly CDN',
                  "Version $lastVersion is available. You are currently running $currentVersion."
                      . ' Please consider upgrading at your earliest convenience.'
              );
              $this->cacheManager->clean([\Magento\Framework\App\Cache\Type\Config::TYPE_IDENTIFIER]);
          }
      }
docs: Check feed for modification
  
  @param null $currentVersion