Block Update Notifications

How to block ALL Software Update Notifications in macOS
Some inexperienced users sometimes accidentally click on the Apple Software Update request in Notifications. These clickable Notifications appear even though all software updates are disabled in System Preferences. - I am maintaining a number of hackintosh systems which I have set up with OpenCore that have such inexperienced users who then need help because something might have to be fixed after an unintentional macOS operating system or security update. I want to have full administrative control over all updates, but Apple does not make this easy. This is especially important for hackintosh systems, but could be relevant for regular Macs as well, especially since the Monterey update from 12.2.1 to 12.3 has caused serious issues with AMD 5000 and 6000 graphics cards for all users. - You may not need this, if you are the only one using your hackintosh and pay close attention to every Notification.

TL;DR

The short answer is to install the LuLu Application Firewall and block the process softwareupdated when prompted. Re-enable it temporarily when you want to do manual updates. I have tested this solution for a few weeks already and it works satisfactorily.
I have researched this topic and asked about it on Stackexchange - Ask Different, but have not found a better solution yet.

Detailed Step-by-Step

If you have previously used Lulu or are using the Little Snitch firewall, you probably do not need this much detail. This guide is mainly intended for first time users of Lulu.
The obvious first step is to completely disable all updates in System Preferences, but surprisingly this alone does not stop the clickable notifications.

Updates Ready to Install - still appears

This Notification has been appearing on many different versions of macOS even after all updates were disabled in System Preferences. A Notification similar to the following also appeared for Monterey 12.3 on a system that did not have Lulu installed yet.

Download and Install Lulu

Objective-See: LuLu Application Firewall - Big Sur is recommended for version 2.4. Also available is version 1.2 for older macOS versions.

Initially enable all firewall prompts

  • Lulu Preferences > Rules > Uncheck All, so that you will see all Firewall prompts initially.

Trigger a Software Update Request

  • System Preferences > Software Updates > Advanced change any update setting to trigger a software update request

Block when asked

Creates this Firewall rule

Disable Software Updates

  • In System Preferences > Software Updates > Advanced - make sure that all software update settings are set to disabled

Wait for the timeout, you should see:

Allow most apps (minimizes unnecessary firewall prompts)

Manually Check for App Updates and/or macOS Updates

  • In Lulu > Rules search for softwareupdated and temporarily allow software updates
  • Double click on the rule and change to Allow

Enable Software Updates Temporarily

  • System Preferences > Software Updates > Advanced activate the items you wish to update

Reenable the Firewall Rule blocking Software Updates

  • In Lulu > Rules search for softwareupdated and block software updates again
  • Double click on the rule and change to Block

Disable Software Updates Again

  • System Preferences > Software Updates > Advanced deactivate all automatic updates again
Note: this method may still not be idiot proof if a user uses System Preferences directly: I have seen the Monterey 12.3 Software Update actually re-appear inside System Preferences after a while in spite of software updates being blocked by the firewall. This may be due to initial caching of the update information. - If you know of ways to make it even more idiot proof, please let me know in the comments.