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.