For installation copy the file "ExportX.xnt" into the XTensions folder of QuarkXPress. This folder can be found within the program folder, except for QuarkXPress 2017/18/19. For QuarkXPress 2017/18/19 there are two possible places for installation (current user/all users, 20xx --> 2017/2018/2019):
For QuarkXPress 2018/19 Pro (App Store) use the following path: