I coded something real quick that should work, to any browse URL add ?exclude=tg.visual-novel
So, for example, all games without visual novels: https://itch.io/games?exclude=tg.visual-novel
Or if you're feeling adventurous, story rich romance games that aren't visual novels: https://itch.io/games/tag-romance/tag-story-rich?exclude=tg.visual-novel