It works! I have a sequencer track for vocals harmonies that I sent to one Virtual Midi Out 1. On the global stack dedicated to my microphone, I inserted a Waves Harmony plugin, set the Midi input to Virtual Midi In 1 and my harmonies are generated!
I’m not sure if the two Virutal Midi sockets are included in VL or if I previously installed another tool to have them…
Anyway, this solves what was lacking the most for my case.
Thank you and stay on that way!