I was just exploring it all and realized that within the settings for each app the Notification Grouping option appears in the same Options section next to Show Previews option.
Interestingly enough on the main Notifications page of Settings there's a global Show Previews setting at the very top that can be changed and would apply to all apps, but for some reason there isn't a Notification Grouping global option present there even though it's basically a similar type of option.
Hopefully this is just an oversight essentially with this option being a newer one and Apple will add it there at some point (hopefully sooner rather than later).
