They intentionally broke ignoring updates. You used to be able to ignore updates through a terminal command so you can keep everything else untouched and still use update notifications or auto-updates for unrelated updates.

Since Catalina, this is intentionally broken, so now you have a constant red badge on the System Preferences icon and regular notifications to update to macOS Big Shit, which in the end causes the user to ignore other updates (like security updates) they would actually want to install.