Are you still on macOS Ventura or Monterey and prefer not to install Sonoma yet? Sadly, the brain trust at Apple have decided that your preferences don't matter. (These are the same people who decided to rename Preferences to Settings and wreck the app.) Instead, you get harassed by frequent notifications imploring you to "Upgrade to macOS Sonoma", notifications that won't take no for an answer. They don't even have no for an answer! And if you click the wrong thing, you'll accidentally, silently install Sonoma.
As always, I'm on the case, stopping the madness. The solution in this case is actually quite simple, one little Terminal command:
defaults write com.apple.SoftwareUpdate MajorOSUserNotificationDate -date "2025-02-07 23:22:47 +0000"
The exact date is not significant, as long as it's sometime in the future. I just took the output of the following command and added one year.
defaults read com.apple.SoftwareUpdate MajorOSUserNotificationDate
I would say that you should send feedback to Apple about how much you hate these notifications, as well as the forced updates, but I'm currently boycotting Feedback Assistant.