I'm also having the same issue as Lili; running Big Sur 11.4 and getting an error message saying the file's "damaged or incomplete". Would greatly appreciate advice or a fix, as I received the game (which looks ADORABLE) as a gift and can't wait to play! Thank you. :)
Because I am impatient I ended up just buying the steam version of the game of mac. It opened and ran perfectly fine! So I've gone ahead and asked for a refund from itch.io and hopefully that'll come through soon. I hope that you'll get a fix soon since the game is truly adorable and well worth playing :)