How it works: You open the .qxp file in QuarkXPress 202x, select File > Export > InDesign Markup Language (IDML). You then open that IDML file in Adobe InDesign CS6 or later.
Before diving into solutions, it is important to understand why this is a problem in the first place. Why can’t you just "save as" a Quark file into an InDesign file? quarkxpress converter