Can't run Ubuntu 20.04 on WSL in VirtualBox

Given what we've discussed in the comments, my personal recommendation would be to stick with WSL1. It covers most of the use-cases of WSL2 by creating a "translation layer" between calls to the Linux kernel API and that of the Windows kernel. WSL2 does go (at least) one step further with virtualization, but that only works well on supported hardware.

As for WSL2, it's possible that you may have more than one problem, but at least one possibility is that you need to enable "Nested Virtualization" in VirtualBox.

WSL2 uses features of the Windows Hyper-V hypervisor to create a virtual machine. Since you are already running Windows 11 in a VirtualBox VM, that means you are "running a VM inside a VM" -- That's "nested virtualization".

Support for this feature was, I believe, added starting with VirtualBox 6.1.4, but you do have to enable it. See this doc page for full details, but to summarize:

• If you are using the VirtualBox Manager GUI, go to the Processor tab and turn on Enable Nested VT-x/AMD-V. Note, as we learned in the comments, that option is grayed out on your VM since your CPU (Core m3-6Y30) doesn't support hardware-based virtualization.

• As an alternative, you should be able to set the option from the command-line using VBoxManage modifyvm vm-name --nested-hw-virt on. This will reportedly "force" virtualization even on unsupported hardware (but I cannot confirm). Note that, from a comment on this answer, "performance is expected to be abysmal" if your CPU does not support the necessary features.