World of EUC

On the file server that stores the VHDX, just right-click it and mount it.  You can then assign a drive letter to it in diskmgmt.  Then you can use TreeSize or whatever on it.

The profile should not be in use at the time, fyi.

"You dont have permission to mount the file" hmm

I remember thats what i was running into last time i tried. even tried copying the VHDX to my C: and mounting it there, same thing

I have seen errors when mounting the VHD only to see that when I check disk management it has actually mounted. Alternatively use frxcontext to mount it.
<https://learn.microsoft.com/en-us/fslogix/disk-management-utility-reference>

Yes, i would think the disk is already mounted somewhere too

you can check OpenFiles on that server and see if you can find out where