While Apple typically encourages users to install the latest version (10.15.7), you can still access the Catalina installer through official channels. How do download Catalina 10.15.0 - Apple Communities
macOS Catalina 10.15 Download and Installation Guide Released in October 2019, macOS Catalina (10.15) marked a turning point for the Mac. It was the first version to drop support for 32-bit applications entirely and the last major release to use the 10.x versioning scheme. Whether you are restoring an older machine or need a specific environment for development, downloading the right version is essential. Official Download Methods catalina 10.15 0 download