org-ml 6.0.1 is now on melpa. Version 6+ includes support for org-mode 9.7, including the much-faster org-element-ast and a few other improvements. Unfortunately, I had to make enough changes that pre-9.7 org-mode is no longer compatible. If you need to use 9.6 or earlier, stick with org-ml 5.x.
This has technically been available on one of the development branches for months. I have not encountered any issues nor have I heard any from anyone else.
