To turn Multitasking features on or off, go to Settings > Home
Screen & Dock > Multitasking, then you can do the following:
Allow Multiple Apps: Turn off if you don’t want to use Slide Over
or Split View.
Picture in Picture: Turn off if you don’t want to use Picture in
Gestures: Turn off if you don’t want to use Multitasking gestures
to see the app switcher, return to the Home screen, and more.
A slew of readers pointed to this after I said I’d prefer iPhone-style one-app-at-a-time multitasking to the convoluted easy-to-make-a-mistake/hard-to-correct-a-mistake split-screen and Slide Over multitasking in iPadOS. iPadOS supports an option that more or less does this — the “Allow Multiple Apps” option mentioned above.
I’m aware of no other graphical user interface that offers a setting like this. The existence of this setting — and that it is not tucked away under Accessibility — feels like proof that Apple knows iPad multitasking is often invoked by accident and can be confusing.