Software updates aren’t displaying in System Preferences
If updates aren’t showing up in macOS in System Preferences → Software Update or there is just a spinning icon displayed, running the following command in Terminal can help to wake up the software update daemon. Make sure to close the System Preferences window before running this command:
sudo launchctl kickstart -k system/com.apple.softwareupdated
Try reopening System Preferences → Software Update and give it 10-15 seconds to check for available updates.