Unlike iPadOS14 and earlier versions, multi-tasking (including split-screen and slide-over views) cannot now be disabled from settings. Multi-tasking has received a significant overhaul with iPadOS15/16, both simplifying its use and introducing new controls.
Key to accessing and controlling (or avoiding) multi-tasking is the small “three-dot” button that is found at the top-centre edge of the visible App windows.
Information and guidance for using multi-tasking can be found in this support page:
Use multitasking on your iPad - Apple Support
The iPad User Guide is a rich source of frequently overlooked information about your iPad and iPadOS. The Guide is available both online using a web browser (such as Safari), or as an Apple Books download:
iPad User Guide - Apple Support
https://books.apple.com/book/id1567104892
The Tips App, installed by default on all new models of iPad, provides a brief introduction - and leads you to the User Guide. In case you missed it, here is a link to the Tips App:
https://apps.apple.com/gb/app/tips/id1069509450
Apple also has a huge YouTube Channel - containing videos and feature guidance:
https://www.youtube.com/user/Apple