Hi,
For itch.io, you don't add files to game.zip.
You make a new .zip (e.g. myvisualnovel-web.zip) that contains all the build directory files (e.g. all the files within myvisualnovel-1.0.0-dists/myvisualnovel-1.0.0-web/), including game.zip (in the end, there is a zip in a zip, e.g. game.zip in myvisualnovel-web.zip).