If you have problems running WSL2 after installing it inside a virtual machine running on Hyper-V you need to enable nested virtualization.
The error looks something like this:
Error: 0x80370102 The virtual machine could not be started because a required feature is not installed.
This can be fixed by running this command on the Hyper-V host
set-VMProcessor -VMName "My virtual machine name" -ExposeVirtualizationExtensions $true