Upload a zip file containing your built game
Read more https://itch.io/docs/creators/html5#common-pitfalls
Example using github pages https://github.com/excaliburjs/ludum-50/blob/main/.github/workflows/main.yml
Be sure to set the correct public url, if you are hosting your game in sub directory like
ludum-50 off the root.
parcel build ./index.html --dist-dir ./dist --public-url /ludum-50