This takes 10-15 minutes. This is the critical step where Apple’s tool builds the bootable recovery system inside your DMG.
Since Apple does not distribute an official ISO file, you must create one from the downloaded "Install macOS Catalina.app" using Terminal: macos catalina 10157 iso download new
hdiutil convert /tmp/Catalina.dmg -format UDTO -o ~/Desktop/macOS_Catalina_10.15.7.iso This takes 10-15 minutes