This is the first 21.9 branch release with support for the the ATLAS-P2-ITK-17 ("step 3", i.e. post Layout Task Force 2) family of geometries.
Currently supports simulation of ITK-17- geometries, and full chain production of ITK-20- ("step 2.2", i.e. Pixel TDR) geometries.
NB that due to e.g. removal of lingering "release local" Xml files, necessary updates for support of newer geometries, and other updates, the results for ITK-20 are not identical to those obtained from 21.9.0.