You might have already read Riamus's post in the other thread but if not I just wanted to let you know that an a21 compatible update has been released a couple of minutes ago. Also, for those who don't have discord, there's a short-term road map for the project:
1-month road map (till end of July)
* Compatibility with A21 (won't take a month)
* Improved feedback for incorrect settings (including fixes for crashes due to wrong settings)
* Bugfixes for rotations and part issue
Obviously, the first item has already been achieved to a significant extent. I admit that this doesn't look super existing but there may be stuff not mentioned in the schedule.