Mac system Catalina will automatically prompt for updates every once in a while, and a red update prompt will be displayed on the system update icon, and notifications will often pop up in the notification center, which will be very annoying.
If you are also troubled by it, then follow the steps below:
1. Open "System Preferences", click "Software Update".
2. Deselect "Automatically keep my Mac up to date".
3. Click the "Advanced" button.
4. Uncheck all check boxes.
4. Click "OK".
5. Exit the system settings, open the terminal command line, and perform the following three steps:
sudo softwareupdate --ignore "macOS Catalina"
defaults write com.apple.systempreferences AttentionPrefBundleIDs 0
killall Dock