Thumbnail view on ipad OS 15 files

Thumbnail view?

I suspect that you 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. 

For example, if you have three running instances of Safari, each with its own set of open tabs, you will see three thumbnails corresponding to each running instance of Safari - plus a button to open a new instance of Safari. Simply tapping a thumbnail will switch directly to that running instance of Safari. 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. Multitasking and the Shelf cannot be disabled in iPadOS15.

No, not the shelf. We are talking about the recent addition of thumbnails of pages of a document when opened from the Files app. A PDF now opens with the main viewing area reduced by thumbnails of all the pages. I used to be able to read my sheet music, but with the thumbnails, reduced main display area makes the document too small to see well.

i want it back the way it was, without thumbnails, and page displayed “full size”.