Hello! I'm not entirely sure what might be causing this issue. I found a few similar questions that may help:
https://itch.io/t/2028448/unable-to-install-a-game-through-itchio-app
https://itch.io/t/4089960/no-compatible-downloads-were-found
According to these posts, it seems that downloading the game through your browser, rather than the itch.io app, may resolve the problem.