Once downloaded, right-click the app and select "Show Package Contents." Navigate to Contents/SharedSupport/ . You will find the SharedSupport.dmg – this is the core disk image containing the bootable system files.
Before installing Mac OS Catalina 10.15.7, ensure that your Mac meets the minimum system requirements: Mac Os Catalina 10.15 7 Dmg Download
Are you looking to create a with this download, or are you just trying to update your current system? Download macOS Catalina 10.15.7 Combo Update Once downloaded, right-click the app and select "Show