hdiutil detach /Volumes/Install\ macOS\ Big\ Sur
hdiutil convert ~/Desktop/BigSur2021.dmg -format UDTO -o ~/Desktop/BigSur2021.iso

2021 — Macos Big Sur Iso

While macOS Big Sur (version 11) officially retired in September 2023, it received a surprise security update (version 11.7.11) as recently as February 2026 to maintain FaceTime and Messages functionality until 2027.

Convert DMG to ISO/CDR

hdiutil convert ~/Desktop/BigSur.dmg -format UDTO -o ~/Desktop/BigSur.iso macos big sur iso 2021

Where to get an official Big Sur 11.2 ISO… - Apple Communities While macOS Big Sur (version 11) officially retired

hdiutil detach /Volumes/Install\ macOS\ Big\ Sur
hdiutil convert ~/Desktop/BigSur2021.dmg -format UDTO -o ~/Desktop/BigSur2021.iso