It looks like you're using the itch app, so I downloaded it and tested it out. The downloads don't show up for me either when I try using the "install" button, and I can't figure out why...
However, you can still access the zip files from the app. Here's how:
First, when you search for Fetch Quest in the app, you should see a "download now" button on the page:
When you click it, it will ask if you want to pay for the game. You don't have to. You can bypass this by clicking "No thanks, just take me to the downloads".
Then you should have the choice to download any of the game files, not just the guide. 
I hope that helps!