As you may know, there have been a lot of major changes from 1.20.2, to 1.20.5/6 and 1.21; which resulted in some power/action/condition/data types that cannot be re-implemented. This is due to the work-arounds being either too unreliable/too hacky, too much of a pain to maintain in the long run, or just outright impossible to do, therefore, we've decided to remove and re-structure stuff to accommodate for the changes.
(Make sure to check this list for updates, I'll be updating this frequently throughout the development of the 1.21 port!)