If you've downloaded it using the Itch app then check how much empty space you have on your computer, the Itch app will download the archive but not extract the files if you don't have enough free space. The game is pretty big but for some reason the extraction process requires a lot more space than the actual game takes, I can't remember exactly how much but I needed to free up more than 10 gigabytes of space to be able to extract it manually.