Here you can follow the guide how to attachconfigure VDI image with VirtualBox.
Use VirtualBox to create an additional disk image that's has at least 60GB of space. Login to your Google account, navigate to the download link, right-click on the file and click on Make a copy.Then shut down machine and started it again. Windows can create and mount VHD disk images through Disk Management. to get it to boot from the CD, I started the VM and then went to Devices menu > CD/DVD Devices > Choose a virtual CD/DVD disk file., then navigated to choose yosemitefixed.dmg. Download Big Sur InstallAssistant.pkg (9GB) either inside the virtual machine or on the host on a disk image that will be mounted on the virtual machine.Select the Mac Os Extended (Journaled) format and continue. step 10 b Select the virtual disk and then click Erase.
Here’s how: step 10 a From the installer menu select Utilities->Disk Utility. Here's how to run macOS Big Sur on VirtualBox: If this happens to you, it means that we’ll need to format your VDI or virtual disk as Mac OS Extended before you can proceed.