Virtualbox stopped working under 20.04 (32-bit Windows guest)

I have to run some Windows XP programs (don't ask why) and VirtualBox has stopped working with this client after upgrading from 18.04. Virtualbox 6.1 is the base version of VirtualBox supported on 20.04 and I suspect that 6.1 requires VT-X support even for a 32-bit OS like XP.

I'm trying to roll back to 6.0.x with no success as it is not in the repositories for 20.04. Any suggestions?