Insert the encrypted device in your Mac. It will tell you it can’t use it and would invite you to initialize it. Just click “Ignore”. Run the disk utility to identify what disk is your encrypted device (probably it will be “disk2”).
Then open a terminal and run the following:
Replace “disk2” by the actual disk for you.
WARNING Don’t get this wrong or you can corrupt your Mac’s hard drive!
In VirtualBox, select your VM and click “Settings”. Then click
“Storage” and “Controller: SATA”. Then click on the “plus” icon next
to “Controller: SATA” (either optical drive or hard disk). Then click
“Choose existing disk”. Click the “Add” button and locate the
“mydevice.vmdk” file. Ensure it is selected and click “Choose”. Then
start your Ubuntu VM and
lsblk should see the new device now.
For some reason, Nautilus doesn’t show it, so I had to set it up manually: