How to remove third column in Finder Windows on macOS 13.5.1?

A couple of days ago the appearance of my Finder windows changed. For decades the Finder windows have consisted of only two columns: the sidebar on the left and the larger window showing the documents in the folder at which I am looking. But recently a third column has appeared to the right of the main column. This third column show a thumbnail of whatever document I have highlighted in the main column of the Finder window.

I do not know what to call this third column. I call it a right-side side bar simply because that is what it looks like to me.

I can close this third column by dragging its left border over to the right side of the Finder window. That gets tedious.

I expect that this "right-side side bar" appeared when I made some errant keystroke while doing something else. I have no idea what this incorrect keystroke might be.

Does anyone recognize what I am trying to describe here? Is there some way to remove this third column from my Finder windows?

I am in MacOS 13.5.1.

[Re-Titled by Moderator]