It looks like you uploaded the zip file for the web version but forgot to tell itch.io that it can be played in the browser.
To do this, you can go to the uploaded files in the "Edit Game" page (which you are already familiar with), and then tick the box saying "This file will be played in the browser" for the web version. You might also have to tick the "SharedArrayBuffer support" checkbox in the "Embed options" section right below the "Uploads" section if you are using Godot 4.
Looking forward to play your submission! :)