If you need a "bootable" version (often why users seek a DMG), follow these steps using a USB drive of at least : macOS Catalina - Technical Specifications - Apple Support
Once your Mac boots into the glorious Catalina desktop: download macos catalina 10157 dmg file install
Once you have the file, the installation process depends on what you downloaded: If using the App Store (Full Installer): Install macOS Catalina /Applications Double-click to launch it and follow the on-screen prompts. If you need to do a "clean install," you should create a bootable USB drive createinstallmedia command in Terminal. If using a DMG Update file: Double-click the file to mount it. Double-click the package installer inside. If you need a "bootable" version (often why
: Open Terminal and run the following command to download the installer directly from Apple's servers: softwareupdate --fetch-full-installer --full-installer-version 10.15.7 3. Create a Bootable USB Installer Double-click the package installer inside
Here are the steps to download the macOS Catalina 10.15.7 .dmg file:
Once completed, the download automatically stops. Close the installer window if it opens immediately. The file is safely located in your labeled as Install macOS Catalina . Method 2: Download DMG Files Directly From Apple
(~4.82 GB): Best for updating from any previous version of Catalina. macOS Catalina 10.15.7 Standard Update