How can I use use MoXF as a VST instrument in Logic Pro X
That is really a Logic Pro X question. As far as I know, Logic does not run VST at all... but instead uses AU protocol.
When you say you want to use the MOXF as a VST we are going to take that to mean, you want to be able to deliver the audio from the MOXF through the same signal path as soft synths... so called “virtual” audio. This means you are monitoring the audio output of the synth rather than routing it to an Audio Track. It remains virtual audio... actual Audio is typically rendered later in a separate Mixdown process.
The advantage of this type of routing is you can process the virtual audio with DAW plugin Effects... and you can monitor with those effects (since actual audio rendering is done separately you are listening to how the signal will sound once you actually EXPORT the mixdown (print the audio to a Track).
The “Yamaha MOXF6/MOXF8 Editor Standalone/VST“ can run in any VST3 compatible DAW (as mentioned Logic Pro is not, as far as I know). The Editor allows you to establish this advanced routing scenario with a DAW, like Cubase AI.
It can be done in Cubase Pro with any external hardware synth and/or Effect processor... most “Pro” DAW software has a way to setup and work with External Instrument and/or Effects with advanced routing, but it is certainly a Logic question on how to set that up.
You want to lookup terms like External Instruments.