Attached is the default mapping for Export to IFC from an iModel - Version 3 - Dated January 2022
In the global section this was added:
/* Process assembly as single IfcEntity (geometric data of all assembled elements will be collected and placed to IfcEntity, properties of child elements will be missing). Default value is false. */ "JoinAssemblies" : "false"
Note that all mapping IFC files should now contain the global variables section.