You appear to have two questions - one outlined in the title of this tread - the other within the body text.
1) Recent Applications
Recent Applications are displayed by default to the right of the iPadOS Dock. This can be disabled in iPad settings:
Settings > Home Screen & App Library > [Dock] Show Suggested & Recent Apps in Dock - set to OFF

2) Mail App - "Little Pages"
You have encountered the iPadOS “Shelf” - this being a fundamental feature of the iPadOS multitasking environment.
Assuming that your iPad is running iPadOS 17.x, you can disable the shelf - but in so doing you will also totally disable iPadOS multitasking:
Settings > Multitasking & Gestures > [Multitasking] - set to OFF

iPadOS permits you to have multiple App windows of the same App - each being self contained. The shelf, when triggered, shows a thumbnail of each Window associated with the App. Each App - such as Mail, Safari, Notes, Calendar, etc. - has its own corresponding shelf.
The Shelf is used to quickly switch between open windows or instances of the App. Individual windows can be closed directly from the Shelf; just swipe the unwanted thumbnail off the top of the screen.
This article from Appleinsider has a useful explanation of this feature:
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