Once you have Install macOS Catalina.app :
Installing the OS on multiple machines without downloading it each time. macos catalina 10.15.7 dmg download
macOS Catalina 10.15.7 was the final version of the Catalina operating system line, released by Apple in September 2020. It remains a critical version for users maintaining older hardware or requiring a specific environment for 32-bit application support (though Catalina itself dropped 32-bit support, the installer is often required for virtualization or downgrade purposes). Once you have Install macOS Catalina