Description of problem:
libvirt does not appear to support the most recent VirtualBox 6.0 API. I didn't see an existing ticket for this and am hoping this is the right place to add one.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. virsh --debug=4 -c vbox:///session
error: failed to connect to the hypervisor
error: internal error: unable to initialize VirtualBox driver API
successful connection to vbox hypervisor
Thanks for the bug report, however, to set realistic expectations I must mention that the vbox driver doesn't have an active maintainer right now. So any support for 6.0 will rely on some motivated developer to step forward to do the work & submit patches to libvirt upstream.