How download Macos Catalina when my computer wants to download Macos Monterey?

Download the macOS upgrade installer app here:  Catalina.

Once downloaded, double-click the “Install macOS Catalina” app in the Applications folder to begin the upgrade.

If your Mac is not compatible with Catalina then your download may be disallowed.

➡️ macOS 10.15 Catalina is compatible with the Macs listed here