The search for a is a search for stability. While Apple wants everyone on the latest OS, professionals and retro-computing enthusiasts know that Big Sur 11.4 (2021) represents the peak of Intel macOS performance before Apple fully pivoted to Apple Silicon.
Alternatively, if you have a legitimate copy from 2021: macos big sur iso 2021
VirtualBox has notoriously poor macOS support. The 2021 Big Sur ISO works where newer ISOs fail because VirtualBox 6.1/7.0 relies on an outdated audio driver (HDA) that Apple removed in Monterey. The search for a is a search for stability
You now have a legitimate, safe ISO file on your desktop suitable for virtual machines. The 2021 Big Sur ISO works where newer
sudo hdiutil attach /tmp/BigSur.dmg -noverify -mountpoint /Volumes/BigSur
hdiutil attach /tmp/BigSur.dmg -noverify -mountpoint /Volumes/BigSurISO 3. Create the Bootable Media Use the built-in createinstallmedia tool to flash the installer files onto your mounted image.