How to get rid of this

The full version of a previously published reply is as follows…

“The three dots “button”, and the multi-tasking controls of which you complain, are a core element of the iPadOS15 User Interface - intended to simplify use of full/split/slide-over multitasking. This control cannot be hidden or suppressed”.

Some Apps may require update, by their respective developers, to accommodate changes made within iPadOS. Until affected Apps are updated, if causing difficulties, there is little that you can do other than to seek assistance from the respective App Developer:

How to contact an app developer - Apple Support

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

Feedback - iPad - Apple

You are very welcome.

You are not the first, nor are likely to be the last, in expressing a dislike for this change. For most, you get used to it after a short while.

I recommend that you make use of the feedback portal.

You can't.

"The three dots “button” is a core element of the iPadOS15 User Interface -

intended to simplify use of full/split/slide-over multitasking.

This control cannot be hidden or suppressed."