virtualbox.org

I can copy a persistent LiveUSB to a vdi file and create a VBox VM from there:

sudo VBoxManage convertfromraw -format VDI /dev/sdd u2004_live.vdi

However, how do I boot a live Linux system directly from a bootable USB device? That is, without first creating a multi-GB VM?

The old-school BIOS provided by Virtualbox does not support booting from USB.

The EFI BIOS might, but your guest OS would require compatibility with EFI, too.

My version of VBox (6.1.6) has the feature to turn on EFI compatibility. The guest system，Ubuntu 20.04LTS，of course, also supports EFI.