I can’t split screen in some app

Third party app developers are responsible for activating multitasking features in iOS for their apps.

The multitasking ability is not a global function of iOS, in and of itself.

Maybe that Bible app doesn't support multitasking or limited multitasking like Slide Over, only.

You may have to contact/leave feedback with the developer of the Bible app you are using.

Good Luck!

I can't split screen between the Settings app and the iOS Notes app, either.

I get the Slide Over screen only.

It is the way it is and the way Apple, in this case, has coded this behaviour.

The only way you know an app has split screen capability is when you get that vertical black bar with a white drag bar inside of it.

Not every app in the iOS App Store is going to support split screen multitasking and even Apple doesn't support in all of the default apps of iOS.

Once again, it is what it is.