I have this exact issue, I wonder if there's an issue with the mac .zip file?
That would be weird, because I can unzip it fine. Things to check include:
- Redownloading the file to ensure it didn't get corrupted during download
- Checking system storage to ensure it can get unzipped fully
- Using a different unzip utility
- Downloading from another source (two mirrors are provided in the game's Patreon) in case it's a problem on itch's servers