The notification API is quite old (iOS 3). It's explicitly an untrusted API that you shouldn't use for something like showing the restore in progress UI, so I suspect that was something written quite a bit later. Widget extensions are iOS 14. There's older ways to run background tasks, but none of them would give the soft brick. Background fetch, for example, originally didn't run until after you launched an app for the first time after restarting.
FWIW I also thought you meant UI notifications (the reason is: I’m dumb). But anyway, I found the point of clarification helpful even though it wasn’t strictly necessary.
