I remember this and thought the apps I was trying to configure had disabled it/it was locked down by one UI 7. This comment made me dig around in settings and I found it for anyone else stuck with one UI.
Notifications > Advanced settings > Manage notification categories for each app (scroll to bottom)
This seems like such a stupid thing to hide in advanced settings when it is enabled by default on older versions but at least it is still available?
I remember when my rats used to sleep like this!