Created a Custom Windows 11 VHD - Mounting the VHD does not assign a drive letter

I created a custom Windows 11 VM as described in Kari's thread, Create Windows 10 ISO image from Existing Installation. Starting with Step 4.6, he shows how to create a custom install.wim. When I mount the AVHDX file associated with the most recent snapshot in Disk Management, the system does not assign a drive letter. Therefore, I cannot proceed with the DISM command (below) to create the WIM as it requires a drive letter for the /capturedir argument.

dism /capture-image /imagefile:D:\install.wim /capturedir:K:\ /name:"AnyName" /compress:maximum /checkintegrity /verify /bootable

This works with my Windows 10 VMs. I cannot even right-click the mount in Disk Management and assign a letter as those options are greyed out. Does anyone know why this is happening and how I can get around this to create my install.wim?

I would try and use the merge option from Hyper-V edit disk menu, and create a NEW vhdx file (merge the checkpoint with parent vhdx file). Then try and mount new vhdx file.

Thanks. I also tried to mount the parent vhdx file (without merging) but that didn't help. I then used Diskpart to assign a letter to the volume and that worked for some reason.

Doesn't deleting the checkpoint also merge the snapshot with the parent... leaving just a vhdx file?