Once the creation process is finished, you unmount the DMG and convert it to a UDIF (ISO) format. hdiutil convert /tmp/Catalina.dmg -format UDTO -o ~/Desktop/Catalina.cdr Finally, rename the .cdr extension to .iso .
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Catalina --nointeraction mac os catalina download iso