You can expand Virtual Disk via Hyper-V UI.
After the expantion, the guest OS might not take the expantion into account.
Check disk partitions :
sudo fdisk -l
If there is an error like the following : "GPT PMBR size mismatch", you need to fix the disk size by expanding the partition to the free size:
# install growpart
sudo apt install cloud-guest-utils
# expand sda1 partition into the free space
sudo growpart /dev/sda 1
# resize
sudo resize2fs /dev/sda1
Credits : https://linguist.is/2020/08/12/expand-ubuntu-disk-after-hyper-v-quick-create/