At 18:00 on 16 September, XProtect 5315 was released for all Macs. Sequoia systems were unable to update for 24 hours, and Tahoe silently updated when it felt like it. How come?
softwareupdated
There should be an update available, but you can’t find it, or it fails to install, or you have problems with a Content Caching Server. How to tackle these.
Opening the settings runs a partial check for updates, but omits important updates, and almost immediately loses its help button.
The Eclectic Light Company 