Expand the VDHX file via Hyper-V as mentioned in existing solutions and then inside the VM:
fdisk -l
See which partition is the current Ubuntu setup – should be obvious based on size (in my case was sda3)
growpart /dev/sda 3
Note the space as mentioned.
pvresize /dev/sda3
This is the step which isn’t mentioned in a lot of places; its the intemediate step that allows the logical volume extension step work.
lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
The /dev/ part can seen in the fdisk output from step 1.
resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv
After the prep above, this step now works. Takes a couple of moments and afterwards can verify with df -h that the partition is expanded.