By enabling WSL 2, VirtualBox VM will be almost unusable at the moment ( June 2020 ).

If you need to migrate existing Windows VM, one of the free option is Hyper-V.

Steps I took:

  • Ensure Hyper-V is installed
  • Export vhd from existing Virtual Box's VM
  • Convert vhd to vhdx
  • Create new instance of VM.
    I use VM generation 1 for this purpose as the VM is Windows 8.1. Attach vhdx to this new instance.

It wasn't the smoothest process, but in the end everything is working.