Stop the Catalina update reminders:

Stop the Catalina update reminders:

1. Launch "System Preferences" >> "Software Update"
2. Click "Advanced"
3. Uncheck "Check for Updates" , "Download New Updates When Available" , and "Install macOS Updates" then "OK"
4. Launch Terminal : "Applications" >> "Utilities" >> "Terminal"
5. Enter the below commands:

sudo softwareupdate --ignore "macOS Catalina"   (for new iOS Big Sur, put "big sur" insted "Catalina" )

defaults write com.apple.systempreferences AttentionPrefBundleIDs 0

killall Dock

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Reference Link: https://www.macworld.com/article/3447396/how-to-stop-getting-a-reminder-to-update-to-catalina-in-macos.html