Apologies if this isn’t technically correct but my understanding is that Vorpx hooks into the directx or openGL graphics systems. unfortunately Vulkan is an entirely different system so Vorpx doesn’t know how to deal with it.
Ralph has stated that if certain games are Vulkan only (as X4 is) then he may look at getting Vorpx to play nice with it. However I imagine this may take some time so don’t hold your breath!