Apple no longer shows Catalina in the main "Software Update" pane unless you are already running Mojave or earlier. For newer Macs, you need the App Store link.
Let me know if you need help creating a bootable installer. 👇 macos catalina 10.15.7 download
Click this link on your Mac: 👉 macappstores://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12 Apple no longer shows Catalina in the main
How to Download macOS Catalina 10.15.7 (Official & Safe Methods) macos catalina 10.15.7 download
That is the final, most stable version of Catalina (released Nov 2020). It includes all security patches before Big Sur.