EDIT: Just to be very sincere and transparent. The content of this post has been removed to avoid further discussion. I do not think my kind of views are welcome in this community.
I'm sorry, but that's just not practical.
It's not quite forced, but you can't explicitly ignore. In practice I'm one accidental click away from an unwanted update now. (Each time need to remember to go one menu level deeper before updating)
nocatalina() {
sudo softwareupdate --ignore "macOS Catalina"
defaults write com.apple.systempreferences AttentionPrefBundleIDs 0
killall Dock
}