Ipad email screen, remove annoying list of emails across bottom of screen

You appear to make reference to the “Shelf” - this being a new feature of the now revised iPadOS multitasking environment. 

iPadOS permits you to have multiple “instances” of the same App - each instance being self contained. The shelf, when triggered, shows a thumbnail of each running instance of an App - or open page within it.

For example, if you have three running instances of Mail, or individual open messages, you will see three thumbnails that correspond to each running instance or open email - plus a button to open another. Simply tapping a thumbnail will switch directly to that open page. Each App has its own corresponding shelf.

This article from Appleinsider has a useful explanation of this new feature along with many of the updates to multitasking:

https://appleinsider.com/articles/21/08/12/how-to-master-multitasking-on-ipad-and-ipad-pro-in-ipados-15

The iPad User Guide is also a rich source of frequently overlooked information. 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

You should note that the shelf is an integral component of the multitasking User Interface. It cannot be disabled.