I would also like this added, I always stumble over what to add them as.
Adventure.
I would say,,,,no. Visual novels are a popular genre, shocked they don't have their own genre here. +1 from me.
I'm not disagreeing that visual novel as a genre should be added as an option on this website. I was addressing OP who was unsure what to categorize visual novel games in how these types of games should be categorized in the meantime.
However, I still am of the opinion that visual novels are a sub-genre to the broad adventure genre.
This post I found explains the idea nicely. Despite this, there are still plenty of visual novels listed that warrant a differentiation to both categories by adding visual novel as an option for users to select.