Steps to block updates to Mac OS X Catalina:
- Open System Preferences by clicking the Apple logo in the upper left corner.
- Go to the App Store and select it. On macOS, you'll now see a number of options for automatic updates.
- To turn off automatic updates, uncheck the box next to Automatically check for updates, which is selected by default.
- Click the empty box next to Automatically check for updates to enable automatic updates. A tick mark will now appear in the box.