A new macOS is like a new app you have never installed, so you will not see it in updates. You have to search for the new macOS Utility app Mojave in the App Store. Try searching for Mojave in the App Store.
I'm sure in previous years the OS update came as a simple App Store update.
Ho Hum things change.
[doublepost=1538151589][/doublepost]Now I know where it is lurking, I'll hang on a while and see how it all settles down and wait until the wrinkles are ironed out before downloading it.
I'm not quite ready for the inevitable ('what the h**l is that, don't like it, how do I get rid of it).