Staudey You don't need the guest-package when you host a VM on that machine
Thanks for all your help. 99.9% of my experience with VirtualBox (years of it) has been on Windows. I was accustomed to updating the guest additions every time I updated VirtualBox. That's probably why I installed it in the first place, in case it was needed.
Other than using it at work, most of what I did with VMs was distro-hopping. I'm done with that, now that I have Solus.
EDIT: And that thanks goes to everyone who helped with this.