When creating a CIM image for MSIX app attach, make sure that you’re using a lower or equal OS version than your target OS in e.g. Azure Virtual Desktop. If you use Windows 11 to create a CIM file and try to mount this on Windows 10, the result will be one of the following.

Azure Portal:

ActivityId: 1ef4d1ad-e4af-42d1-b6fa-139c45775efb Error: The MSIX Application metadata expand request failed on all Session Hosts that it was sent to. Session Host: xxxx1, Error: Native error when mounting CIM, HResult -2147024809, ErrorCode 87.. (Code: 400)

Using the CimDiskImage PS module:

Mount-CimDiskimage : Mounting xxxxx.cim to volume failed with Error:'The operation completed successfully Errorcode:0'

Mount-CimDiskimage : Mounting xxxx.cim to volume failed with Error:'Too many posts were made to a semaphore ErrorCode:298'

Above happens because W10 using V2 CIM disks, while W11 uses V3 CIM disks.