If the link doesn't work, search the Mac App Store for "macOS Catalina" – it should still appear as "Get".
If you need for compatibility with older 32-bit apps or legacy hardware, here is the official way to get it from Apple. macos catalina 10.15.7 download
How to Download macOS Catalina 10.15.7 (Official & Safe Methods) If the link doesn't work, search the Mac
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. If the link doesn't work