Hardware has arrived.
Refurb Dell T7610 Workstation and a shiny new laptop.
Kali/Windows dual-boot on the laptop is working like a champ.
I intended to use the Dell as a host for virtual machines from VulnHub, which mostly has VirtualBox machines (at least the few that I spot-checked).
Looking at VirtualBox’s website, I saw downloads for Debian 10.
Long story short, that didn’t work at all.
I managed to mangle up my sources.list file (but, hey, I learned what that thing is for!), and then restore it, but VirtualBox just wouldn’t install
Ultimately I discovered that Debian doesn’t officially support VirtualBox since 2015 (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=794466).