By using a hardware cloning tool, it probably copied over the partitions. Which is a small one for EFI boot, one or two which have the Linux and the actual UmbrelOS in them, and one for storage. The storage one will be cloned as the same size as it was in the previous drive.
So I think you need to get the new one and expand the partition to include the empty space.
Or maybe it’s a different issue. Try inspecting the drive with the ‘Disks’ utility to see the partition sizes.