So, breakdown of why things have taken so long:
First, the build service we use for Mac builds (Travis) was
undergoing gigantic delay problems with several thousand build jobs queued up and builds taking hours and hours to complete. We use Travis to do builds because doing everything to get a proper build, including signing, is a pain to do manually. The Travis build is automated to do all of this for us, and at the time we weren't sure if it was worth trying to do by hand anyway, since we didn't know how long the backlog really was. This took several days to clear up.
In the meantime, we had to restart the build several times because we were having problems getting Python scripting working. For some reason, we weren't able to get the Mac to recognize local Python 3.6 installs. After some time of trying to get this working with no success, we decided that we should just ship without Python scripting support for now. Lua scripting still works fine.
However, right before we shipped, we noticed an issue with Qt themes not rendering correctly. Several default styles were not applying correctly and even "native" UI components were looking very ugly (like, Windows 98 ugly). We still have not figured out why Qt is not building or copying correctly on Travis to make these appear, as local unsigned builds seem to work just fine. Hopefully this issue will be resolved quickly and we can get v21 into your hands.