Macbooks won't apply updates unless you leave them plugged in overnight. If you do the totally normal thing of not charging a full battery, you get to enjoy the riveting experience of watching a slow update screen 30 minutes after you next use it.
But you don’t have to, macOS, AFAIK, will always ask you before it reboots into the logo-and-progress-bar update screen. Even if you manually launch the update, after it finishes the Preparing stage, it will again warn you that the machine is about to reboot, and gives you the option to cancel that. I’m genuinely curious about the sequence that leads to macOS forcing an update on you, I’ve never had that happen in my 10 years on a Mac.
