Yeah, Itch only allows zip-file.. but, You have to go to the option of "kind of project" in the edit page of your game and you have to change the kind from HTML to downloadable. And in your zip-file updated you have to select "executable" and click on the button with the windows icon. Also, you have to deselect the option that say "this file will be played in the browser". So the people not will exit of your game page for not see a game in the browser and this people go to the download links directly.