I just tried a VB install (version 6), and gave up....
Followed the steps to create the vdi file, but then got lost.....couldn't figure out how to install the guest OS.
It is harder than parallels. Effectively, you create the VM, and then you have to point it to an .iso of the OS installer in its virtual CD drive, it boots from the iso, and then you use the installers disk utility to format the virtual drive, and install to it.
Biggest problem I ran into, was that I created the iso from the downloaded full installer, but when VB booted from it, it kept doing a remote install from Apple's servers.
To solve that, I had to recreate the .iso from an "install macos (whatever)" that was on a bootable USB stick.
I had the trial of Parallels a few years ago, and it seemed so much easier to setup, suppose that's what your paying for.
You just selected the OS download and it setup.
Unless you subscribe, parallels is limied to 4 cores and 4gb of memory, also, parallels doesn't offer multiple displays for the guest OS.
My goal was to virtualise my 3 display system, so I could effectively swipe to a space that's an older version of macOS. I'm still not sure if it can be done.
I'm assuming any left behind files won't hurt.
I just moved the Application and Prefs folder to the trash.
I used AppCleaner to remove Parallels - there's some com. etc files that get picked up as well.