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I found I needed it for the basic Acrobat Reader from Adobe - but there might be a setting available in there that I don't know about. In any case, I didn't see anything wrong with providing more options.

In Acrobat Reader, it's in the menu "View" -> "Page Display" -> "Show Cover Page in Two Page View".

Unfortunately, in Acrobat Reader there's no button and no keyboard shortcut for it, you got to use the menu. That's one reason why I prefer other PDF readers (PDF-XChange Editor on Windows and Foxit on macOS).