I’ve tried creating MacOS 10.x VMs in VirtualBox before, with partial success, but nothing was worth using.
The post https://techsprobe.com/install-macos-big-sur-on-virtualbox-on-windows-pc/ was pretty much on-point for creating a MacOS 11.0 (Big Sur) VM in VirtualBox. My experience was that there were a couple of deviations required from the script.
First, the SATA storage controller setting required the “Use Host UI Cache” option to be checked on as the Big Sur installation process failed to launch with it unchecked.
Second, the Big Sur Disk Utility program was unable to perform the “Erase” function required to initialize the disk for MacOS when the VM’s VHD storage type was Dynamic. A fixed-size disk was required.
As of now, the OS seems stable and I was able to upgrade to MacOS 12 Monterrey as well.