Kinda funny how this is true but there's a line of Mac OSes that can't connect to the App Store anymore so you can't upgrade the OS without manually downloading it off of an Apple help page.
It's not the end of the world, but I've had to help more than one person walk through this process cuz they're like "I can't update the OS????"
I was a Mac admin when they pushed the change to move Updates into the Mac App Store and I hated it then. It didn't even make sense from an ill-advised "must match iOS" way, since OS updates happened in Settings.app on that platform. Just bone-headed "this will boost eNgAgEmEnT" BS.
And it's hard to even find the download links, and a lot of them don't work.