The Osiris Camera has been indispensable for the past ten years
If you are on a Mac running macOS 10.15 or later, you can bypass the App Store and use the Terminal to download the full installer:
A direct DMG is most useful when creating a bootable installer. Here’s how: Macos Catalina Dmg Direct Download
If you specifically need a DMG file for archival or a virtual machine, you must create it manually from the file you downloaded. Microsoft Community Hub How To Create A Bootable MacOS Catalina Install Drive If you are on a Mac running macOS 10
The Internet Archive hosts a legitimate macOS Catalina.dmg from an Apple mirror. The SHA-1 checksum for version 10.15.7 (19H15) is: e6b10f5c4126fdb783b1e776f5c93a0e2fec6a2f Macos Catalina Dmg Direct Download
The Osiris Camera has been indispensable for the past ten years