The Kunena team has announce the arrival of Kunena 6.3.0 [K 6.3.0] in stable which is now available for download as a native Joomla extension for J! 4.4.x/5.0.x/5.1.x. This version addresses most of the issues that were discovered in K 6.2 and issues discovered during the last development stages of K 6.3
In previous versions of Kunena I was able to access Kunena classes by including the file JPATH_LIBRARIES.'/kunena/bootstrap.php' this file no longer exists in K6.
I have tried including the JPATH_ROOT . '/administrator/components/com_kunena/api/api.php' file and I get an error on missing Kunena classes. I tried booting the application, and I tried including the autoloader: JPATH_LIBRARIES . '/kunena/External/autoload.php'
Nothing seems to work. Attempting to use any of the KunenaForum classes fail. I do have all of the use statements included.
My external script is extending the Joomla\CMS\Application\WebApplication and other J! related calls are working fine.
I was able to get my script to run by creating an autoloader function for the Kunena libraries, but there should be a standard way to bootstrap Kunena for library access.