Having the same problem here.
Recent community posts
I wasn't presented with that button on the download page. I don't know why but itch.io sometimes have problem with this where the button would be missing. I've attached a screenshot of my download page. Could you email the key to me?
I purchased with my registered itch.io account. The download page for this order only has a direct download link, doesn't have the steam key button which is usually there if steam keys are included. I checked my email, it just directs me to the same download page. Am I missing anything?