How to get my iPad to full screen using safari
How can I get my iPad back to full screen
You may find these overview Apple video guides to be helpful:
After viewing, you’ll be ready for the additional Multitasking Guide:
https://support.apple.com/en-us/HT207582
The iPad User Guide for iPadOS is also a rich source of information. Here are links to both the downloadable and online versions of the Guide:
https://help.apple.com/epub/ipad/en/
https://support.apple.com/guide/ipad/welcome/ipados
I hope this explanation and additional information is helpful in resolving any difficulties you may be having with Multitasking features of your iPad.