VST (Virtual Studio Technology) is the plug-in standard innovated by Steinberg back in 1996... open to all manufacturers of synth (Instrument) and effect processing plug-in software. Your question really has nothing to do with the MX or Cubase, but understanding you were given a free license for Prologue when you purchased the MX, we understand.
VST Instrument and VST Effects run in any compatible DAW software.
What you need to do is contact the makers of FL Studio and find out if your version FL STUDIO is VST3 compatible.
Prologue is a VST3 Plug-in... and will run inside all VST3 compatible DAWs. Most pro DAW software can... when you install a VST plug-in its data is placed so your DAW can access it and allow it to run.