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you will need to enable hardware virt like the dialog notes. something like https://docs.oracle.com/en/virtualization/virtualbox/6.0/admin/nested-virt.html as it looks like your host is virtualbox

I do have this selected. I tried rebooting my machine but still get the same pop up box.

may want to poke around https://documentation.ubuntu.com/server/how-to/virtualisation/enable-nested-virtualisation/ to see if you have setup your Ubuntu VM to support it as well