Applies to-  Mac only.

Solution-

  1. Quit QuarkXPress 2018 Pro (if opened).
  2. Navigate to Go menu (Desktop) >> (Press and hold down the option/alt key) Library >> Containers >> com.quark.QuarkXPress 2018.pro >> Data >> Library >> Preferences >> Quark
  3. Under Quark, rename the folder named "QuarkXPress 2018" to "Old_QuarkXPress 2018".