In the PDM search tool there was the option to split the preview screen Horiz or Vert. With out 2017 upgrade it is not available.
Under View on the toolbar "Split" is listed, but greyed out.
Works fine for me, 2017 SP4
Are you in the search tool? Below is where I would like to split my view, but do not have the PDM toolbar to access the Display menu you show. Which is available in the explorer search window. There is a Split under the View, but like I said it is greyed out.
Scrap that, I see the same thing as you in the search tool, but accord to the help that split is something else that doesn't look very useful...
If you set the option (vertical or horizontal) in the windows explorer embedded search (in Charley's Screenshot > under display) it will change the behaviour in the separate search tool as well (you may need to close and reopen it)
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