: Apple provides .dmg files for individual updates (like the Catalina 10.15.7 Update ), but these require a version of Catalina to already be installed and are not full OS installers. Creating a DMG from the Installer
This writes the full bootable installer onto the DMG volume. After it finishes, eject the DMG, and you have a bootable DMG file. Download Macos 10.15 Catalina Dmg File
If you are looking to download the , the most reliable and secure way to do so is through official Apple channels. How to Download macOS Catalina : Apple provides