I think I have spawned some confusion here. There is no way to both ignore Catalina updates while still presenting badges [notification] for other updates or system preferences alerts. Some other posters who have claimed otherwise have either disabled notifications for all software updates or simply meant that software update can be set to permanently ignore Catalina related updates (although it will still present a badge, in that regard yes, sudo softwareupdate —ignore ‘macOS Catalina’ works).
The commands by both posts each contain elements of necessary steps. The command to softwareupdate —ignore is critical. The other steps are measures I think were intended to block notifications. Notification badges can be permanently blocked using a different command.
The following can be used to both ignore Catalina update and permanently block notification badges (for all software updates):
Code:
killall "System Preferences"
sudo softwareupdate --ignore 'macOS Catalina'
defaults write com.apple.systempreferences AttentionPrefBundleIDs 0
killall Dock
To re-enable badges for system prefs, change the 0 to 1.