Currently (March 2020), the XV4 64-bit version of Q++Studio supports all QuarkXPress versions, from 8 to 2019, inclusively.
However, not all versions of QuarkXPress are supported by all versions of Windows.
Quark-Windows Restrictions and Incompatibilities
QuarkXPress 8 can only run on Windows 7 (i.e. not on Windows 10).
Additionally, Quark does not officially support QuarkXPress 2019 on Windows 7 (although our own tests, using QuarkXPress 2019 with Windows 7, showed no problems, and we plan to support QuarkXPress 2019 on Windows 7, insofar as it pertains to Q++Studio).