In previous versions of macOS, you could get the Nag Bubble to go away by entering this in Terminal when System Preferences was not running:
defaults write com.apple.systempreferences AttentionPrefBundleIDs 0
I have a Keyboard Maestro macro that runs that every time System Preferences.app quits on my Mojave machine.
Sometimes it still shows up if you go awhile without running System Preferences.
Super annoying and bad behavior from Apple that they 100% should not do.