If you because of a restore suddenly get stuck with one “disk0.vhdx” and one “disk0-snapshot.vhdx” virtual disk, and you are not able to merge them using Hyper-V Manager?

You can merge them with PowerShell

Merge-VHD -Path *PathToSnapshotFile*\disk0-snapshot.vhd -DestinationPath *PathToDestinationFile*\disk0.vhd

ex:

Merge-VHD -Path c:\VM\VM01\Virtual Hard Disks\disk0-snapshot.vhd -DestinationPath c:\VM\VM01\Virtual Hard Disks\disk0.vhd