iOS 15 update blues

The Sidebar is now closed with the Sidebar button at top-left of the screen:

Note: For this button to be visible, if Bookmarks/Reading List/History is displayed in the sidebar, you must first tap the “Safari” button that appears in this location.

There are many changes within iPadOS15 - and changes to Safari and its management of Bookmarks is only one of the significant changes. 

Many would concur with your observation concerning the the revised iPadOS15 Safari Sidebar. Here is just one of the many discussions about this topic:

https://discussions.apple.com/thread/253208195?answerId=256003346022

Apple do invite constructive feedback, comments and feature requests via their product feedback pages. For iPad and iPadOS:

Feedback - iPad - Apple

You are encouraged to make use of this facility in expressing your views concerning issues, bugs, or functionality changes of which you are unhappy.

This is an incompetent change to LANDSCAPE mode on iPad.

In portrait mode the bookmarks bar appears in front, so you can dismiss it but touching the webpage (which is darkened). Great! Works fine.

But in Landscape, it acts completely different, taking up permanent space on the left (no darkened webpage) UNTIL you press the top left button several times, depending on how deep you are in your path of bookmark folders. ie. the more folders within folders, the more times you have to press the bloody button!

APPLE! Please darken the webpage and make the bookmark sidebar temporary like in portrait!

This is very inefficient— for an update that is trying to simplify your browser experience by putting the address bar on the bottom of the screen to speed up browsing time I don’t understand why apple would have it so you have to back through several folder layers just to get rid of the bookmarks tab in landscape mode.

Or put the bookmarks icon back on the right of the < button.