VirtualBox fails to start
I suspected, after reading OP's own answer, that my activation of Windows Hello PIN had hosed my VirtualBox install; even when attempting to set up brand new VMs, they all failed to start with the same error. I instead decided to try a different tack though: I reinstalled VirtualBox (over the top of my old install).
My old version was 6.1.18, and I reinstalled 6.1.30 over it -- as soon as the install had completed (I had to reinstall the VirtualBox Extension Pack as well because the old one was out of date) I tried to fire up a VM, and boom, it runs like a champ!