Disabling updates in Catalina

Hey guys - Wondering if there are any ways to get rid of the daily MacOS update notifications by brute force. Under software updates in system preferences, I have long had "check for updates" unchecked and "automatically keep my Mac up to date" unchecked, but it just doesn't stop the notifications. While I can excuse the notifications for a day, I accidentally hit the install button 2 weeks ago, saw no way to cancel it, and have gotten OpenCore error messages intermittently on boot up since that time ("OCB: StartImage failed"). I know there are apparently fixes for this error and I just need to make the time to do it, but in the meantime, how do I stop Apple updates? Can I make a firewall rule blocking Apple servers or anything? It's absurd how pesky MacOS can be. :/