Those only turn off auto updating not update notifications, which you could argue should be an option, but I disagree people are entirely too good at not looking for updates if they don’t have too (out of sight out of mind and all).
If you click on the left side of the notification, it opens System Preferences, which you can just close again or ignore. However, while this avoids setting any attempt to update overnight, it doesn't actually stop you from getting another prompt the next day or whatever.
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.
Huh? You set exactly if, how and when to update in System Preferences.
You can set it to never, always, to ask, to download but not install, etc.
It's been that way for as long as I can remember, and Big Sur doesn't appear to have changed anything. All the checkboxes are still there.