This is a term I haven’t heard before. Upon googling, I found this site which explains vulnerable narcissism:
https://www.choosingtherapy.com/vulnerable-narcissist/Cluster B diagnoses share many attributes. The psychologist I saw individually some years after my husband and I attended couples counseling with her, told me that he has a personality disorder. When I asked her to specify, she demurred, stating that Cluster B personality disorders can be fluid, with varying attributes.
It made sense to me, as I had noticed he presented more like a narcissist with her, while at home, I observed the borderline traits, and occasionally the histrionic ones too.
The tools you can learn here (see the Tools section at the top of this page) will help you deal with individuals with Cluster B disorders as well as be helpful with emotionally healthy people.