Quote please add VirtualBox to bookworm-fasttrack (#51) · Issues · Debian Fast Track / Support · GitLab
Just in case you didn’t notice, bookworm has been supported in the official repos since 18-Jul-2023.
https://download.virtualbox.org/virtualbox/debian/dists/bookworm/
Although I prefer to wait for the fasttrack version, as it’s usually better integrated with the system.