Mustangproject 2.5.2, released 2022-07-09, adds support to also validate XRechnung 2.2 (CII) files, a new build profile and improved Order-X and Factur-X(thanks to Weclapp-Dev) XML.
The german B2G invoice CIUS, XRechnung, is set to mandatorily switch to version 2.2 as of August 2022.