I ended up having to compile each OS version with the matching XCode. Build three times, once each for Catalina, BigSur and Monterey. Each with a different version of XCode (11, 12 and 13) using EXPORT DEVELOPER_DIR=/pathto/XCode-NN etc before the xcodebuild

Can you elaborate on how ChildDext is defined? Also, how to set up the child dext to send and receive data from the parent dext? In our KEXT we had a virtual interface (the parent) and each USB Device instance passes data to and from the virtual interface. Thanks!