Create a blank disk image file by running: hdiutil create -o /tmp/Catalina -size 8500m -volname Catalina -layout SPUD -fs HFS+J
Addresses a graphics issue on iMac (Retina 5K, 27-inch, 2020) with Radeon Pro 5700 XT.
file for a virtual machine or bootable USB, you must use the createinstallmedia
This is the most secure method for a full OS install. You can access it via this direct App Store link Apple Support (DMG Updates):